JavaScript: Deep comparison recursively: Objects and properties

JavaScript: Deep comparison recursively: Objects and properties - javascript

Today I finished reading Ch. 4 in Eloquent JS and I'm struggling to understand how to perform a deep comparison between objects and their properties, particularly through the use of a recursive call. I know my solution below is quite naive and a bit bulky, but I'm trying to wrap my head around all these new things I'm still learning! Just less than a month in on programming :) I would appreciate any tips and help you might have in improving the code and also if you could help me better understand the recursion that needs to occur. Thank you in advance!
Question (Eloquent JS 2nd Ed, Chapter 4, Exercise 4):
Write a function, deepEqual, that takes two values and returns true
only if they are the same value or are objects with the same
properties whose values are also equal when compared with a recursive
call to deepEqual.
Test Cases:
var obj = {here: {is: "an"}, object: 2};
var obj1 = {here: {is: "an"}, object: 2};
console.log(deepEqual(obj,obj1));
My Code:
function objectTester(x) {
if (typeof x === 'object' && x !== null)
return true;
}
function deepEqual(valOne, valTwo) {
if (valOne === valTwo) return true;
var comp1 = objectTester(valOne);
var comp2 = objectTester(valTwo);
if (comp1 === comp2) {
var count1;
var count2;
for (var prop in valOne) {
count1++
return count1;
}
for (var prop in valTwo) {
count2++
return count2;
}
if (count1 === count2) {
// This is where I'm getting stuck, not sure how I can recurisvely compare
// two arguments that are to be compared.
}
}

Probably easiest to just post a function that does the job with plenty of comments. The recursive part is near the bottom, in the function passed to every:
// Helper to return a value's internal object [[Class]]
// That this returns [object Type] even for primitives
function getClass(obj) {
return Object.prototype.toString.call(obj);
}
/*
** #param a, b - values (Object, RegExp, Date, etc.)
** #returns {boolean} - true if a and b are the object or same primitive value or
** have the same properties with the same values
*/
function objectTester(a, b) {
// If a and b reference the same value, return true
if (a === b) return true;
// If a and b aren't the same type, return false
if (typeof a != typeof b) return false;
// Already know types are the same, so if type is number
// and both NaN, return true
if (typeof a == 'number' && isNaN(a) && isNaN(b)) return true;
// Get internal [[Class]]
var aClass = getClass(a);
var bClass = getClass(b)
// Return false if not same class
if (aClass != bClass) return false;
// If they're Boolean, String or Number objects, check values
if (aClass == '[object Boolean]' || aClass == '[object String]' || aClass == '[object Number]') {
return a.valueOf() == b.valueOf();
}
// If they're RegExps, Dates or Error objects, check stringified values
if (aClass == '[object RegExp]' || aClass == '[object Date]' || aClass == '[object Error]') {
return a.toString() == b.toString();
}
// Otherwise they're Objects, Functions or Arrays or some kind of host object
if (typeof a == 'object' || typeof a == 'function') {
// For functions, check stringigied values are the same
// Almost certainly false if a and b aren't trivial
// and are different functions
if (aClass == '[object Function]' && a.toString() != b.toString()) return false;
var aKeys = Object.keys(a);
var bKeys = Object.keys(b);
// If they don't have the same number of keys, return false
if (aKeys.length != bKeys.length) return false;
// Check they have the same keys
if (!aKeys.every(function(key){return b.hasOwnProperty(key)})) return false;
// Check key values - uses ES5 Object.keys
return aKeys.every(function(key){
return objectTester(a[key], b[key])
});
}
return false;
}
The tests on Date, RegExp, Error, etc. should probably return false if the values/strings aren't the same then fall through to the property checks, but do that only if you think someone might attach properties to Number objects (it's extremely rare to use Number objects, much less add properties to them, but I guess it might happen).
Here it is:
/*
** #param a, b - values (Object, RegExp, Date, etc.)
** #returns {boolean} - true if a and b are the object or same primitive value or
** have the same properties with the same values
*/
function objectTester(a, b) {
// If a and b reference the same value, return true
if (a === b) return true;
// If a and b aren't the same type, return false
if (typeof a != typeof b) return false;
// Already know types are the same, so if type is number
// and both NaN, return true
if (typeof a == 'number' && isNaN(a) && isNaN(b)) return true;
// Get internal [[Class]]
var aClass = getClass(a);
var bClass = getClass(b)
// Return false if not same class
if (aClass != bClass) return false;
// If they're Boolean, String or Number objects, check values
if (aClass == '[object Boolean]' || aClass == '[object String]' || aClass == '[object Number]') {
if (a.valueOf() != b.valueOf()) return false;
}
// If they're RegExps, Dates or Error objects, check stringified values
if (aClass == '[object RegExp]' || aClass == '[object Date]' || aClass == '[object Error]') {
if (a.toString() != b.toString()) return false;
}
// For functions, check stringigied values are the same
// Almost impossible to be equal if a and b aren't trivial
// and are different functions
if (aClass == '[object Function]' && a.toString() != b.toString()) return false;
// For all objects, (including Objects, Functions, Arrays and host objects),
// check the properties
var aKeys = Object.keys(a);
var bKeys = Object.keys(b);
// If they don't have the same number of keys, return false
if (aKeys.length != bKeys.length) return false;
// Check they have the same keys
if (!aKeys.every(function(key){return b.hasOwnProperty(key)})) return false;
// Check key values - uses ES5 Object.keys
return aKeys.every(function(key){
return objectTester(a[key], b[key])
});
return false;
}

You can use below code for deep comparison -
const isEqual = (a, b) => {
if (a === b) return true;
if (a instanceof Date && b instanceof Date) return a.getTime() === b.getTime();
if (!a || !b || (typeof a !== 'object' && typeof b !== 'object')) return a === b;
if (a === null || a === undefined || b === null || b === undefined) return false;
if (a.prototype !== b.prototype) return false;
let keys = Object.keys(a);
if (keys.length !== Object.keys(b).length) return false;
return keys.every(k => isEqual(a[k], b[k]));
};
example -
isEqual({ prop1: [2, { e: 3 }], prop2: [4], prop3: 'foo' }, { prop1: [2, { e: 3 }], prop2: [4], prop3: 'foo' }); // true

Check the code below. That should work for you.
function objectEquals(x, y) {
'use strict';
if (x === null || x === undefined || y === null || y === undefined) { return x === y; }
// after this just checking type of one would be enough
if (x.constructor !== y.constructor) { return false; }
// if they are functions, they should exactly refer to same one (because of closures)
if (x instanceof Function) { return x === y; }
// if they are regexps, they should exactly refer to same one (it is hard to better equality check on current ES)
if (x instanceof RegExp) { return x === y; }
if (x === y || x.valueOf() === y.valueOf()) { return true; }
if (Array.isArray(x) && x.length !== y.length) { return false; }
// if they are dates, they must had equal valueOf
if (x instanceof Date) { return false; }
// if they are strictly equal, they both need to be object at least
if (!(x instanceof Object)) { return false; }
if (!(y instanceof Object)) { return false; }
// recursive object equality check
var p = Object.keys(x);
return Object.keys(y).every(function (i) { return p.indexOf(i) !== -1; }) &&
p.every(function (i) { return objectEquals(x[i], y[i]); });
}

I think all given answers are amazing.
But for not so experts eyes I will like to make reading easier clarifying how the solutions that use Array.prototype.every works for nested arrays.
It turns out that the keys method from the global Object has a not so commonly used capability where receive an array as parameter and
returns an array whose elements are strings corresponding to the
enumerable properties found directly upon object.
console.log(typeof [] === 'object') // true
Object.keys([true, { a:'a', b: 'b' }, 2, null]) // ['0', '1', '2', '3']
So this is how Object.keys().every() works fine for function arguments, indexing {}s and []s, either with property keys or array indexes.
Hope help someone.

Related

Count object literal duplicates in an array [duplicate]

This question already has answers here:
How to determine equality for two JavaScript objects?
(82 answers)
Closed 6 years ago.
What is the best way to compare objects in JavaScript?
Example:
var user1 = {name : "nerd", org: "dev"};
var user2 = {name : "nerd", org: "dev"};
var eq = user1 == user2;
alert(eq); // gives false
I know that two objects are equal if they refer to the exact same object, but is there a way to check if they have the same attributes' values?
The following way works for me, but is it the only possibility?
var eq = Object.toJSON(user1) == Object.toJSON(user2);
alert(eq); // gives true

Unfortunately there is no perfect way, unless you use _proto_ recursively and access all non-enumerable properties, but this works in Firefox only.
So the best I can do is to guess usage scenarios.
1) Fast and limited.
Works when you have simple JSON-style objects without methods and DOM nodes inside:
JSON.stringify(obj1) === JSON.stringify(obj2)
The ORDER of the properties IS IMPORTANT, so this method will return false for following objects:
x = {a: 1, b: 2};
y = {b: 2, a: 1};
2) Slow and more generic.
Compares objects without digging into prototypes, then compares properties' projections recursively, and also compares constructors.
This is almost correct algorithm:
function deepCompare () {
var i, l, leftChain, rightChain;
function compare2Objects (x, y) {
var p;
// remember that NaN === NaN returns false
// and isNaN(undefined) returns true
if (isNaN(x) && isNaN(y) && typeof x === 'number' && typeof y === 'number') {
return true;
}
// Compare primitives and functions.
// Check if both arguments link to the same object.
// Especially useful on the step where we compare prototypes
if (x === y) {
return true;
}
// Works in case when functions are created in constructor.
// Comparing dates is a common scenario. Another built-ins?
// We can even handle functions passed across iframes
if ((typeof x === 'function' && typeof y === 'function') ||
(x instanceof Date && y instanceof Date) ||
(x instanceof RegExp && y instanceof RegExp) ||
(x instanceof String && y instanceof String) ||
(x instanceof Number && y instanceof Number)) {
return x.toString() === y.toString();
}
// At last checking prototypes as good as we can
if (!(x instanceof Object && y instanceof Object)) {
return false;
}
if (x.isPrototypeOf(y) || y.isPrototypeOf(x)) {
return false;
}
if (x.constructor !== y.constructor) {
return false;
}
if (x.prototype !== y.prototype) {
return false;
}
// Check for infinitive linking loops
if (leftChain.indexOf(x) > -1 || rightChain.indexOf(y) > -1) {
return false;
}
// Quick checking of one object being a subset of another.
// todo: cache the structure of arguments[0] for performance
for (p in y) {
if (y.hasOwnProperty(p) !== x.hasOwnProperty(p)) {
return false;
}
else if (typeof y[p] !== typeof x[p]) {
return false;
}
}
for (p in x) {
if (y.hasOwnProperty(p) !== x.hasOwnProperty(p)) {
return false;
}
else if (typeof y[p] !== typeof x[p]) {
return false;
}
switch (typeof (x[p])) {
case 'object':
case 'function':
leftChain.push(x);
rightChain.push(y);
if (!compare2Objects (x[p], y[p])) {
return false;
}
leftChain.pop();
rightChain.pop();
break;
default:
if (x[p] !== y[p]) {
return false;
}
break;
}
}
return true;
}
if (arguments.length < 1) {
return true; //Die silently? Don't know how to handle such case, please help...
// throw "Need two or more arguments to compare";
}
for (i = 1, l = arguments.length; i < l; i++) {
leftChain = []; //Todo: this can be cached
rightChain = [];
if (!compare2Objects(arguments[0], arguments[i])) {
return false;
}
}
return true;
}
Known issues (well, they have very low priority, probably you'll never notice them):
objects with different prototype structure but same projection
functions may have identical text but refer to different closures
Tests: passes tests are from How to determine equality for two JavaScript objects?.

Here is my ES3 commented solution (gory details after the code):
function object_equals( x, y ) {
if ( x === y ) return true;
// if both x and y are null or undefined and exactly the same
if ( ! ( x instanceof Object ) || ! ( y instanceof Object ) ) return false;
// if they are not strictly equal, they both need to be Objects
if ( x.constructor !== y.constructor ) return false;
// they must have the exact same prototype chain, the closest we can do is
// test there constructor.
for ( var p in x ) {
if ( ! x.hasOwnProperty( p ) ) continue;
// other properties were tested using x.constructor === y.constructor
if ( ! y.hasOwnProperty( p ) ) return false;
// allows to compare x[ p ] and y[ p ] when set to undefined
if ( x[ p ] === y[ p ] ) continue;
// if they have the same strict value or identity then they are equal
if ( typeof( x[ p ] ) !== "object" ) return false;
// Numbers, Strings, Functions, Booleans must be strictly equal
if ( ! object_equals( x[ p ], y[ p ] ) ) return false;
// Objects and Arrays must be tested recursively
}
for ( p in y )
if ( y.hasOwnProperty( p ) && ! x.hasOwnProperty( p ) )
return false;
// allows x[ p ] to be set to undefined
return true;
}
In developing this solution, I took a particular look at corner cases, efficiency, yet trying to yield a simple solution that works, hopefully with some elegance. JavaScript allows both null and undefined properties and objects have prototypes chains that can lead to very different behaviors if not checked.
First I have chosen to not extend Object.prototype, mostly because null could not be one of the objects of the comparison and that I believe that null should be a valid object to compare with another. There are also other legitimate concerns noted by others regarding the extension of Object.prototype regarding possible side effects on other's code.
Special care must taken to deal the possibility that JavaScript allows object properties can be set to undefined, i.e. there exists properties which values are set to undefined. The above solution verifies that both objects have the same properties set to undefined to report equality. This can only be accomplished by checking the existence of properties using Object.hasOwnProperty( property_name ). Also note that JSON.stringify() removes properties that are set to undefined, and that therefore comparisons using this form will ignore properties set to the value undefined.
Functions should be considered equal only if they share the same reference, not just the same code, because this would not take into account these functions prototype. So comparing the code string does not work to guaranty that they have the same prototype object.
The two objects should have the same prototype chain, not just the same properties. This can only be tested cross-browser by comparing the constructor of both objects for strict equality. ECMAScript 5 would allow to test their actual prototype using Object.getPrototypeOf(). Some web browsers also offer a __proto__ property that does the same thing. A possible improvement of the above code would allow to use one of these methods whenever available.
The use of strict comparisons is paramount here because 2 should not be considered equal to "2.0000", nor false should be considered equal to null, undefined, or 0.
Efficiency considerations lead me to compare for equality of properties as soon as possible. Then, only if that failed, look for the typeof these properties. The speed boost could be significant on large objects with lots of scalar properties.
No more that two loops are required, the first to check properties from the left object, the second to check properties from the right and verify only existence (not value), to catch these properties which are defined with the undefined value.
Overall this code handles most corner cases in only 16 lines of code (without comments).
Update (8/13/2015). I have implemented a better version, as the function value_equals() that is faster, handles properly corner cases such as NaN and 0 different than -0, optionally enforcing objects' properties order and testing for cyclic references, backed by more than 100 automated tests as part of the Toubkal project test suite.

Utils.compareObjects = function(o1, o2){
for(var p in o1){
if(o1.hasOwnProperty(p)){
if(o1[p] !== o2[p]){
return false;
}
}
}
for(var p in o2){
if(o2.hasOwnProperty(p)){
if(o1[p] !== o2[p]){
return false;
}
}
}
return true;
};
Simple way to compare ONE-LEVEL only objects.

Certainly not the only way - you could prototype a method (against Object here but I certainly wouldn't suggest using Object for live code) to replicate C#/Java style comparison methods.
Edit, since a general example seems to be expected:
Object.prototype.equals = function(x)
{
for(p in this)
{
switch(typeof(this[p]))
{
case 'object':
if (!this[p].equals(x[p])) { return false }; break;
case 'function':
if (typeof(x[p])=='undefined' || (p != 'equals' && this[p].toString() != x[p].toString())) { return false; }; break;
default:
if (this[p] != x[p]) { return false; }
}
}
for(p in x)
{
if(typeof(this[p])=='undefined') {return false;}
}
return true;
}
Note that testing methods with toString() is absolutely not good enough but a method which would be acceptable is very hard because of the problem of whitespace having meaning or not, never mind synonym methods and methods producing the same result with different implementations. And the problems of prototyping against Object in general.

The following algorithm will deal with self-referential data structures, numbers, strings, dates, and of course plain nested javascript objects:
Objects are considered equivalent when
They are exactly equal per === (String and Number are unwrapped first to ensure 42 is equivalent to Number(42))
or they are both dates and have the same valueOf()
or they are both of the same type and not null and...
they are not objects and are equal per == (catches numbers/strings/booleans)
or, ignoring properties with undefined value they have the same properties all of which are considered recursively equivalent.
Functions are not considered identical by function text. This test is insufficient because functions may have differing closures. Functions are only considered equal if === says so (but you could easily extend that equivalent relation should you choose to do so).
Infinite loops, potentially caused by circular datastructures, are avoided. When areEquivalent attempts to disprove equality and recurses into an object's properties to do so, it keeps track of the objects for which this sub-comparison is needed. If equality can be disproved, then some reachable property path differs between the objects, and then there must be a shortest such reachable path, and that shortest reachable path cannot contain cycles present in both paths; i.e. it is OK to assume equality when recursively comparing objects. The assumption is stored in a property areEquivalent_Eq_91_2_34, which is deleted after use, but if the object graph already contains such a property, behavior is undefined. The use of such a marker property is necessary because javascript doesn't support dictionaries using arbitrary objects as keys.
function unwrapStringOrNumber(obj) {
return (obj instanceof Number || obj instanceof String
? obj.valueOf()
: obj);
}
function areEquivalent(a, b) {
a = unwrapStringOrNumber(a);
b = unwrapStringOrNumber(b);
if (a === b) return true; //e.g. a and b both null
if (a === null || b === null || typeof (a) !== typeof (b)) return false;
if (a instanceof Date)
return b instanceof Date && a.valueOf() === b.valueOf();
if (typeof (a) !== "object")
return a == b; //for boolean, number, string, xml
var newA = (a.areEquivalent_Eq_91_2_34 === undefined),
newB = (b.areEquivalent_Eq_91_2_34 === undefined);
try {
if (newA) a.areEquivalent_Eq_91_2_34 = [];
else if (a.areEquivalent_Eq_91_2_34.some(
function (other) { return other === b; })) return true;
if (newB) b.areEquivalent_Eq_91_2_34 = [];
else if (b.areEquivalent_Eq_91_2_34.some(
function (other) { return other === a; })) return true;
a.areEquivalent_Eq_91_2_34.push(b);
b.areEquivalent_Eq_91_2_34.push(a);
var tmp = {};
for (var prop in a)
if(prop != "areEquivalent_Eq_91_2_34")
tmp[prop] = null;
for (var prop in b)
if (prop != "areEquivalent_Eq_91_2_34")
tmp[prop] = null;
for (var prop in tmp)
if (!areEquivalent(a[prop], b[prop]))
return false;
return true;
} finally {
if (newA) delete a.areEquivalent_Eq_91_2_34;
if (newB) delete b.areEquivalent_Eq_91_2_34;
}
}

I wrote this piece of code for object comparison, and it seems to work. check the assertions:
function countProps(obj) {
var count = 0;
for (k in obj) {
if (obj.hasOwnProperty(k)) {
count++;
}
}
return count;
};
function objectEquals(v1, v2) {
if (typeof(v1) !== typeof(v2)) {
return false;
}
if (typeof(v1) === "function") {
return v1.toString() === v2.toString();
}
if (v1 instanceof Object && v2 instanceof Object) {
if (countProps(v1) !== countProps(v2)) {
return false;
}
var r = true;
for (k in v1) {
r = objectEquals(v1[k], v2[k]);
if (!r) {
return false;
}
}
return true;
} else {
return v1 === v2;
}
}
assert.isTrue(objectEquals(null,null));
assert.isFalse(objectEquals(null,undefined));
assert.isTrue(objectEquals("hi","hi"));
assert.isTrue(objectEquals(5,5));
assert.isFalse(objectEquals(5,10));
assert.isTrue(objectEquals([],[]));
assert.isTrue(objectEquals([1,2],[1,2]));
assert.isFalse(objectEquals([1,2],[2,1]));
assert.isFalse(objectEquals([1,2],[1,2,3]));
assert.isTrue(objectEquals({},{}));
assert.isTrue(objectEquals({a:1,b:2},{a:1,b:2}));
assert.isTrue(objectEquals({a:1,b:2},{b:2,a:1}));
assert.isFalse(objectEquals({a:1,b:2},{a:1,b:3}));
assert.isTrue(objectEquals({1:{name:"mhc",age:28}, 2:{name:"arb",age:26}},{1:{name:"mhc",age:28}, 2:{name:"arb",age:26}}));
assert.isFalse(objectEquals({1:{name:"mhc",age:28}, 2:{name:"arb",age:26}},{1:{name:"mhc",age:28}, 2:{name:"arb",age:27}}));
assert.isTrue(objectEquals(function(x){return x;},function(x){return x;}));
assert.isFalse(objectEquals(function(x){return x;},function(y){return y+2;}));

I have modified a bit the code above. for me 0 !== false and null !== undefined. If you do not need such strict check remove one "=" sign in "this[p] !== x[p]" inside the code.
Object.prototype.equals = function(x){
for (var p in this) {
if(typeof(this[p]) !== typeof(x[p])) return false;
if((this[p]===null) !== (x[p]===null)) return false;
switch (typeof(this[p])) {
case 'undefined':
if (typeof(x[p]) != 'undefined') return false;
break;
case 'object':
if(this[p]!==null && x[p]!==null && (this[p].constructor.toString() !== x[p].constructor.toString() || !this[p].equals(x[p]))) return false;
break;
case 'function':
if (p != 'equals' && this[p].toString() != x[p].toString()) return false;
break;
default:
if (this[p] !== x[p]) return false;
}
}
return true;
}
Then I have tested it with next objects:
var a = {a: 'text', b:[0,1]};
var b = {a: 'text', b:[0,1]};
var c = {a: 'text', b: 0};
var d = {a: 'text', b: false};
var e = {a: 'text', b:[1,0]};
var f = {a: 'text', b:[1,0], f: function(){ this.f = this.b; }};
var g = {a: 'text', b:[1,0], f: function(){ this.f = this.b; }};
var h = {a: 'text', b:[1,0], f: function(){ this.a = this.b; }};
var i = {
a: 'text',
c: {
b: [1, 0],
f: function(){
this.a = this.b;
}
}
};
var j = {
a: 'text',
c: {
b: [1, 0],
f: function(){
this.a = this.b;
}
}
};
var k = {a: 'text', b: null};
var l = {a: 'text', b: undefined};
a==b expected true; returned true
a==c expected false; returned false
c==d expected false; returned false
a==e expected false; returned false
f==g expected true; returned true
h==g expected false; returned false
i==j expected true; returned true
d==k expected false; returned false
k==l expected false; returned false

Here is my version, pretty much stuff from this thread is integrated (same counts for the test cases):
Object.defineProperty(Object.prototype, "equals", {
enumerable: false,
value: function (obj) {
var p;
if (this === obj) {
return true;
}
// some checks for native types first
// function and sring
if (typeof(this) === "function" || typeof(this) === "string" || this instanceof String) {
return this.toString() === obj.toString();
}
// number
if (this instanceof Number || typeof(this) === "number") {
if (obj instanceof Number || typeof(obj) === "number") {
return this.valueOf() === obj.valueOf();
}
return false;
}
// null.equals(null) and undefined.equals(undefined) do not inherit from the
// Object.prototype so we can return false when they are passed as obj
if (typeof(this) !== typeof(obj) || obj === null || typeof(obj) === "undefined") {
return false;
}
function sort (o) {
var result = {};
if (typeof o !== "object") {
return o;
}
Object.keys(o).sort().forEach(function (key) {
result[key] = sort(o[key]);
});
return result;
}
if (typeof(this) === "object") {
if (Array.isArray(this)) { // check on arrays
return JSON.stringify(this) === JSON.stringify(obj);
} else { // anyway objects
for (p in this) {
if (typeof(this[p]) !== typeof(obj[p])) {
return false;
}
if ((this[p] === null) !== (obj[p] === null)) {
return false;
}
switch (typeof(this[p])) {
case 'undefined':
if (typeof(obj[p]) !== 'undefined') {
return false;
}
break;
case 'object':
if (this[p] !== null
&& obj[p] !== null
&& (this[p].constructor.toString() !== obj[p].constructor.toString()
|| !this[p].equals(obj[p]))) {
return false;
}
break;
case 'function':
if (this[p].toString() !== obj[p].toString()) {
return false;
}
break;
default:
if (this[p] !== obj[p]) {
return false;
}
}
};
}
}
// at least check them with JSON
return JSON.stringify(sort(this)) === JSON.stringify(sort(obj));
}
});
Here is my TestCase:
assertFalse({}.equals(null));
assertFalse({}.equals(undefined));
assertTrue("String", "hi".equals("hi"));
assertTrue("Number", new Number(5).equals(5));
assertFalse("Number", new Number(5).equals(10));
assertFalse("Number+String", new Number(1).equals("1"));
assertTrue([].equals([]));
assertTrue([1,2].equals([1,2]));
assertFalse([1,2].equals([2,1]));
assertFalse([1,2].equals([1,2,3]));
assertTrue(new Date("2011-03-31").equals(new Date("2011-03-31")));
assertFalse(new Date("2011-03-31").equals(new Date("1970-01-01")));
assertTrue({}.equals({}));
assertTrue({a:1,b:2}.equals({a:1,b:2}));
assertTrue({a:1,b:2}.equals({b:2,a:1}));
assertFalse({a:1,b:2}.equals({a:1,b:3}));
assertTrue({1:{name:"mhc",age:28}, 2:{name:"arb",age:26}}.equals({1:{name:"mhc",age:28}, 2:{name:"arb",age:26}}));
assertFalse({1:{name:"mhc",age:28}, 2:{name:"arb",age:26}}.equals({1:{name:"mhc",age:28}, 2:{name:"arb",age:27}}));
assertTrue("Function", (function(x){return x;}).equals(function(x){return x;}));
assertFalse("Function", (function(x){return x;}).equals(function(y){return y+2;}));
var a = {a: 'text', b:[0,1]};
var b = {a: 'text', b:[0,1]};
var c = {a: 'text', b: 0};
var d = {a: 'text', b: false};
var e = {a: 'text', b:[1,0]};
var f = {a: 'text', b:[1,0], f: function(){ this.f = this.b; }};
var g = {a: 'text', b:[1,0], f: function(){ this.f = this.b; }};
var h = {a: 'text', b:[1,0], f: function(){ this.a = this.b; }};
var i = {
a: 'text',
c: {
b: [1, 0],
f: function(){
this.a = this.b;
}
}
};
var j = {
a: 'text',
c: {
b: [1, 0],
f: function(){
this.a = this.b;
}
}
};
var k = {a: 'text', b: null};
var l = {a: 'text', b: undefined};
assertTrue(a.equals(b));
assertFalse(a.equals(c));
assertFalse(c.equals(d));
assertFalse(a.equals(e));
assertTrue(f.equals(g));
assertFalse(h.equals(g));
assertTrue(i.equals(j));
assertFalse(d.equals(k));
assertFalse(k.equals(l));

If you work without the JSON library, maybe this will help you out:
Object.prototype.equals = function(b) {
var a = this;
for(i in a) {
if(typeof b[i] == 'undefined') {
return false;
}
if(typeof b[i] == 'object') {
if(!b[i].equals(a[i])) {
return false;
}
}
if(b[i] != a[i]) {
return false;
}
}
for(i in b) {
if(typeof a[i] == 'undefined') {
return false;
}
if(typeof a[i] == 'object') {
if(!a[i].equals(b[i])) {
return false;
}
}
if(a[i] != b[i]) {
return false;
}
}
return true;
}
var a = {foo:'bar', bar: {blub:'bla'}};
var b = {foo:'bar', bar: {blub:'blob'}};
alert(a.equals(b)); // alert's a false

if you want to check for methods explicitly you can use the method.toSource() or method.toString() methods.

arr.includes() not finding object in array [duplicate]

This question already has answers here:
How to determine equality for two JavaScript objects?
(82 answers)
Closed 6 years ago.
What is the best way to compare objects in JavaScript?
Example:
var user1 = {name : "nerd", org: "dev"};
var user2 = {name : "nerd", org: "dev"};
var eq = user1 == user2;
alert(eq); // gives false
I know that two objects are equal if they refer to the exact same object, but is there a way to check if they have the same attributes' values?
The following way works for me, but is it the only possibility?
var eq = Object.toJSON(user1) == Object.toJSON(user2);
alert(eq); // gives true

Unfortunately there is no perfect way, unless you use _proto_ recursively and access all non-enumerable properties, but this works in Firefox only.
So the best I can do is to guess usage scenarios.
1) Fast and limited.
Works when you have simple JSON-style objects without methods and DOM nodes inside:
JSON.stringify(obj1) === JSON.stringify(obj2)
The ORDER of the properties IS IMPORTANT, so this method will return false for following objects:
x = {a: 1, b: 2};
y = {b: 2, a: 1};
2) Slow and more generic.
Compares objects without digging into prototypes, then compares properties' projections recursively, and also compares constructors.
This is almost correct algorithm:
function deepCompare () {
var i, l, leftChain, rightChain;
function compare2Objects (x, y) {
var p;
// remember that NaN === NaN returns false
// and isNaN(undefined) returns true
if (isNaN(x) && isNaN(y) && typeof x === 'number' && typeof y === 'number') {
return true;
}
// Compare primitives and functions.
// Check if both arguments link to the same object.
// Especially useful on the step where we compare prototypes
if (x === y) {
return true;
}
// Works in case when functions are created in constructor.
// Comparing dates is a common scenario. Another built-ins?
// We can even handle functions passed across iframes
if ((typeof x === 'function' && typeof y === 'function') ||
(x instanceof Date && y instanceof Date) ||
(x instanceof RegExp && y instanceof RegExp) ||
(x instanceof String && y instanceof String) ||
(x instanceof Number && y instanceof Number)) {
return x.toString() === y.toString();
}
// At last checking prototypes as good as we can
if (!(x instanceof Object && y instanceof Object)) {
return false;
}
if (x.isPrototypeOf(y) || y.isPrototypeOf(x)) {
return false;
}
if (x.constructor !== y.constructor) {
return false;
}
if (x.prototype !== y.prototype) {
return false;
}
// Check for infinitive linking loops
if (leftChain.indexOf(x) > -1 || rightChain.indexOf(y) > -1) {
return false;
}
// Quick checking of one object being a subset of another.
// todo: cache the structure of arguments[0] for performance
for (p in y) {
if (y.hasOwnProperty(p) !== x.hasOwnProperty(p)) {
return false;
}
else if (typeof y[p] !== typeof x[p]) {
return false;
}
}
for (p in x) {
if (y.hasOwnProperty(p) !== x.hasOwnProperty(p)) {
return false;
}
else if (typeof y[p] !== typeof x[p]) {
return false;
}
switch (typeof (x[p])) {
case 'object':
case 'function':
leftChain.push(x);
rightChain.push(y);
if (!compare2Objects (x[p], y[p])) {
return false;
}
leftChain.pop();
rightChain.pop();
break;
default:
if (x[p] !== y[p]) {
return false;
}
break;
}
}
return true;
}
if (arguments.length < 1) {
return true; //Die silently? Don't know how to handle such case, please help...
// throw "Need two or more arguments to compare";
}
for (i = 1, l = arguments.length; i < l; i++) {
leftChain = []; //Todo: this can be cached
rightChain = [];
if (!compare2Objects(arguments[0], arguments[i])) {
return false;
}
}
return true;
}
Known issues (well, they have very low priority, probably you'll never notice them):
objects with different prototype structure but same projection
functions may have identical text but refer to different closures
Tests: passes tests are from How to determine equality for two JavaScript objects?.

Here is my ES3 commented solution (gory details after the code):
function object_equals( x, y ) {
if ( x === y ) return true;
// if both x and y are null or undefined and exactly the same
if ( ! ( x instanceof Object ) || ! ( y instanceof Object ) ) return false;
// if they are not strictly equal, they both need to be Objects
if ( x.constructor !== y.constructor ) return false;
// they must have the exact same prototype chain, the closest we can do is
// test there constructor.
for ( var p in x ) {
if ( ! x.hasOwnProperty( p ) ) continue;
// other properties were tested using x.constructor === y.constructor
if ( ! y.hasOwnProperty( p ) ) return false;
// allows to compare x[ p ] and y[ p ] when set to undefined
if ( x[ p ] === y[ p ] ) continue;
// if they have the same strict value or identity then they are equal
if ( typeof( x[ p ] ) !== "object" ) return false;
// Numbers, Strings, Functions, Booleans must be strictly equal
if ( ! object_equals( x[ p ], y[ p ] ) ) return false;
// Objects and Arrays must be tested recursively
}
for ( p in y )
if ( y.hasOwnProperty( p ) && ! x.hasOwnProperty( p ) )
return false;
// allows x[ p ] to be set to undefined
return true;
}
In developing this solution, I took a particular look at corner cases, efficiency, yet trying to yield a simple solution that works, hopefully with some elegance. JavaScript allows both null and undefined properties and objects have prototypes chains that can lead to very different behaviors if not checked.
First I have chosen to not extend Object.prototype, mostly because null could not be one of the objects of the comparison and that I believe that null should be a valid object to compare with another. There are also other legitimate concerns noted by others regarding the extension of Object.prototype regarding possible side effects on other's code.
Special care must taken to deal the possibility that JavaScript allows object properties can be set to undefined, i.e. there exists properties which values are set to undefined. The above solution verifies that both objects have the same properties set to undefined to report equality. This can only be accomplished by checking the existence of properties using Object.hasOwnProperty( property_name ). Also note that JSON.stringify() removes properties that are set to undefined, and that therefore comparisons using this form will ignore properties set to the value undefined.
Functions should be considered equal only if they share the same reference, not just the same code, because this would not take into account these functions prototype. So comparing the code string does not work to guaranty that they have the same prototype object.
The two objects should have the same prototype chain, not just the same properties. This can only be tested cross-browser by comparing the constructor of both objects for strict equality. ECMAScript 5 would allow to test their actual prototype using Object.getPrototypeOf(). Some web browsers also offer a __proto__ property that does the same thing. A possible improvement of the above code would allow to use one of these methods whenever available.
The use of strict comparisons is paramount here because 2 should not be considered equal to "2.0000", nor false should be considered equal to null, undefined, or 0.
Efficiency considerations lead me to compare for equality of properties as soon as possible. Then, only if that failed, look for the typeof these properties. The speed boost could be significant on large objects with lots of scalar properties.
No more that two loops are required, the first to check properties from the left object, the second to check properties from the right and verify only existence (not value), to catch these properties which are defined with the undefined value.
Overall this code handles most corner cases in only 16 lines of code (without comments).
Update (8/13/2015). I have implemented a better version, as the function value_equals() that is faster, handles properly corner cases such as NaN and 0 different than -0, optionally enforcing objects' properties order and testing for cyclic references, backed by more than 100 automated tests as part of the Toubkal project test suite.

Utils.compareObjects = function(o1, o2){
for(var p in o1){
if(o1.hasOwnProperty(p)){
if(o1[p] !== o2[p]){
return false;
}
}
}
for(var p in o2){
if(o2.hasOwnProperty(p)){
if(o1[p] !== o2[p]){
return false;
}
}
}
return true;
};
Simple way to compare ONE-LEVEL only objects.

Certainly not the only way - you could prototype a method (against Object here but I certainly wouldn't suggest using Object for live code) to replicate C#/Java style comparison methods.
Edit, since a general example seems to be expected:
Object.prototype.equals = function(x)
{
for(p in this)
{
switch(typeof(this[p]))
{
case 'object':
if (!this[p].equals(x[p])) { return false }; break;
case 'function':
if (typeof(x[p])=='undefined' || (p != 'equals' && this[p].toString() != x[p].toString())) { return false; }; break;
default:
if (this[p] != x[p]) { return false; }
}
}
for(p in x)
{
if(typeof(this[p])=='undefined') {return false;}
}
return true;
}
Note that testing methods with toString() is absolutely not good enough but a method which would be acceptable is very hard because of the problem of whitespace having meaning or not, never mind synonym methods and methods producing the same result with different implementations. And the problems of prototyping against Object in general.

The following algorithm will deal with self-referential data structures, numbers, strings, dates, and of course plain nested javascript objects:
Objects are considered equivalent when
They are exactly equal per === (String and Number are unwrapped first to ensure 42 is equivalent to Number(42))
or they are both dates and have the same valueOf()
or they are both of the same type and not null and...
they are not objects and are equal per == (catches numbers/strings/booleans)
or, ignoring properties with undefined value they have the same properties all of which are considered recursively equivalent.
Functions are not considered identical by function text. This test is insufficient because functions may have differing closures. Functions are only considered equal if === says so (but you could easily extend that equivalent relation should you choose to do so).
Infinite loops, potentially caused by circular datastructures, are avoided. When areEquivalent attempts to disprove equality and recurses into an object's properties to do so, it keeps track of the objects for which this sub-comparison is needed. If equality can be disproved, then some reachable property path differs between the objects, and then there must be a shortest such reachable path, and that shortest reachable path cannot contain cycles present in both paths; i.e. it is OK to assume equality when recursively comparing objects. The assumption is stored in a property areEquivalent_Eq_91_2_34, which is deleted after use, but if the object graph already contains such a property, behavior is undefined. The use of such a marker property is necessary because javascript doesn't support dictionaries using arbitrary objects as keys.
function unwrapStringOrNumber(obj) {
return (obj instanceof Number || obj instanceof String
? obj.valueOf()
: obj);
}
function areEquivalent(a, b) {
a = unwrapStringOrNumber(a);
b = unwrapStringOrNumber(b);
if (a === b) return true; //e.g. a and b both null
if (a === null || b === null || typeof (a) !== typeof (b)) return false;
if (a instanceof Date)
return b instanceof Date && a.valueOf() === b.valueOf();
if (typeof (a) !== "object")
return a == b; //for boolean, number, string, xml
var newA = (a.areEquivalent_Eq_91_2_34 === undefined),
newB = (b.areEquivalent_Eq_91_2_34 === undefined);
try {
if (newA) a.areEquivalent_Eq_91_2_34 = [];
else if (a.areEquivalent_Eq_91_2_34.some(
function (other) { return other === b; })) return true;
if (newB) b.areEquivalent_Eq_91_2_34 = [];
else if (b.areEquivalent_Eq_91_2_34.some(
function (other) { return other === a; })) return true;
a.areEquivalent_Eq_91_2_34.push(b);
b.areEquivalent_Eq_91_2_34.push(a);
var tmp = {};
for (var prop in a)
if(prop != "areEquivalent_Eq_91_2_34")
tmp[prop] = null;
for (var prop in b)
if (prop != "areEquivalent_Eq_91_2_34")
tmp[prop] = null;
for (var prop in tmp)
if (!areEquivalent(a[prop], b[prop]))
return false;
return true;
} finally {
if (newA) delete a.areEquivalent_Eq_91_2_34;
if (newB) delete b.areEquivalent_Eq_91_2_34;
}
}

I wrote this piece of code for object comparison, and it seems to work. check the assertions:
function countProps(obj) {
var count = 0;
for (k in obj) {
if (obj.hasOwnProperty(k)) {
count++;
}
}
return count;
};
function objectEquals(v1, v2) {
if (typeof(v1) !== typeof(v2)) {
return false;
}
if (typeof(v1) === "function") {
return v1.toString() === v2.toString();
}
if (v1 instanceof Object && v2 instanceof Object) {
if (countProps(v1) !== countProps(v2)) {
return false;
}
var r = true;
for (k in v1) {
r = objectEquals(v1[k], v2[k]);
if (!r) {
return false;
}
}
return true;
} else {
return v1 === v2;
}
}
assert.isTrue(objectEquals(null,null));
assert.isFalse(objectEquals(null,undefined));
assert.isTrue(objectEquals("hi","hi"));
assert.isTrue(objectEquals(5,5));
assert.isFalse(objectEquals(5,10));
assert.isTrue(objectEquals([],[]));
assert.isTrue(objectEquals([1,2],[1,2]));
assert.isFalse(objectEquals([1,2],[2,1]));
assert.isFalse(objectEquals([1,2],[1,2,3]));
assert.isTrue(objectEquals({},{}));
assert.isTrue(objectEquals({a:1,b:2},{a:1,b:2}));
assert.isTrue(objectEquals({a:1,b:2},{b:2,a:1}));
assert.isFalse(objectEquals({a:1,b:2},{a:1,b:3}));
assert.isTrue(objectEquals({1:{name:"mhc",age:28}, 2:{name:"arb",age:26}},{1:{name:"mhc",age:28}, 2:{name:"arb",age:26}}));
assert.isFalse(objectEquals({1:{name:"mhc",age:28}, 2:{name:"arb",age:26}},{1:{name:"mhc",age:28}, 2:{name:"arb",age:27}}));
assert.isTrue(objectEquals(function(x){return x;},function(x){return x;}));
assert.isFalse(objectEquals(function(x){return x;},function(y){return y+2;}));

I have modified a bit the code above. for me 0 !== false and null !== undefined. If you do not need such strict check remove one "=" sign in "this[p] !== x[p]" inside the code.
Object.prototype.equals = function(x){
for (var p in this) {
if(typeof(this[p]) !== typeof(x[p])) return false;
if((this[p]===null) !== (x[p]===null)) return false;
switch (typeof(this[p])) {
case 'undefined':
if (typeof(x[p]) != 'undefined') return false;
break;
case 'object':
if(this[p]!==null && x[p]!==null && (this[p].constructor.toString() !== x[p].constructor.toString() || !this[p].equals(x[p]))) return false;
break;
case 'function':
if (p != 'equals' && this[p].toString() != x[p].toString()) return false;
break;
default:
if (this[p] !== x[p]) return false;
}
}
return true;
}
Then I have tested it with next objects:
var a = {a: 'text', b:[0,1]};
var b = {a: 'text', b:[0,1]};
var c = {a: 'text', b: 0};
var d = {a: 'text', b: false};
var e = {a: 'text', b:[1,0]};
var f = {a: 'text', b:[1,0], f: function(){ this.f = this.b; }};
var g = {a: 'text', b:[1,0], f: function(){ this.f = this.b; }};
var h = {a: 'text', b:[1,0], f: function(){ this.a = this.b; }};
var i = {
a: 'text',
c: {
b: [1, 0],
f: function(){
this.a = this.b;
}
}
};
var j = {
a: 'text',
c: {
b: [1, 0],
f: function(){
this.a = this.b;
}
}
};
var k = {a: 'text', b: null};
var l = {a: 'text', b: undefined};
a==b expected true; returned true
a==c expected false; returned false
c==d expected false; returned false
a==e expected false; returned false
f==g expected true; returned true
h==g expected false; returned false
i==j expected true; returned true
d==k expected false; returned false
k==l expected false; returned false

Here is my version, pretty much stuff from this thread is integrated (same counts for the test cases):
Object.defineProperty(Object.prototype, "equals", {
enumerable: false,
value: function (obj) {
var p;
if (this === obj) {
return true;
}
// some checks for native types first
// function and sring
if (typeof(this) === "function" || typeof(this) === "string" || this instanceof String) {
return this.toString() === obj.toString();
}
// number
if (this instanceof Number || typeof(this) === "number") {
if (obj instanceof Number || typeof(obj) === "number") {
return this.valueOf() === obj.valueOf();
}
return false;
}
// null.equals(null) and undefined.equals(undefined) do not inherit from the
// Object.prototype so we can return false when they are passed as obj
if (typeof(this) !== typeof(obj) || obj === null || typeof(obj) === "undefined") {
return false;
}
function sort (o) {
var result = {};
if (typeof o !== "object") {
return o;
}
Object.keys(o).sort().forEach(function (key) {
result[key] = sort(o[key]);
});
return result;
}
if (typeof(this) === "object") {
if (Array.isArray(this)) { // check on arrays
return JSON.stringify(this) === JSON.stringify(obj);
} else { // anyway objects
for (p in this) {
if (typeof(this[p]) !== typeof(obj[p])) {
return false;
}
if ((this[p] === null) !== (obj[p] === null)) {
return false;
}
switch (typeof(this[p])) {
case 'undefined':
if (typeof(obj[p]) !== 'undefined') {
return false;
}
break;
case 'object':
if (this[p] !== null
&& obj[p] !== null
&& (this[p].constructor.toString() !== obj[p].constructor.toString()
|| !this[p].equals(obj[p]))) {
return false;
}
break;
case 'function':
if (this[p].toString() !== obj[p].toString()) {
return false;
}
break;
default:
if (this[p] !== obj[p]) {
return false;
}
}
};
}
}
// at least check them with JSON
return JSON.stringify(sort(this)) === JSON.stringify(sort(obj));
}
});
Here is my TestCase:
assertFalse({}.equals(null));
assertFalse({}.equals(undefined));
assertTrue("String", "hi".equals("hi"));
assertTrue("Number", new Number(5).equals(5));
assertFalse("Number", new Number(5).equals(10));
assertFalse("Number+String", new Number(1).equals("1"));
assertTrue([].equals([]));
assertTrue([1,2].equals([1,2]));
assertFalse([1,2].equals([2,1]));
assertFalse([1,2].equals([1,2,3]));
assertTrue(new Date("2011-03-31").equals(new Date("2011-03-31")));
assertFalse(new Date("2011-03-31").equals(new Date("1970-01-01")));
assertTrue({}.equals({}));
assertTrue({a:1,b:2}.equals({a:1,b:2}));
assertTrue({a:1,b:2}.equals({b:2,a:1}));
assertFalse({a:1,b:2}.equals({a:1,b:3}));
assertTrue({1:{name:"mhc",age:28}, 2:{name:"arb",age:26}}.equals({1:{name:"mhc",age:28}, 2:{name:"arb",age:26}}));
assertFalse({1:{name:"mhc",age:28}, 2:{name:"arb",age:26}}.equals({1:{name:"mhc",age:28}, 2:{name:"arb",age:27}}));
assertTrue("Function", (function(x){return x;}).equals(function(x){return x;}));
assertFalse("Function", (function(x){return x;}).equals(function(y){return y+2;}));
var a = {a: 'text', b:[0,1]};
var b = {a: 'text', b:[0,1]};
var c = {a: 'text', b: 0};
var d = {a: 'text', b: false};
var e = {a: 'text', b:[1,0]};
var f = {a: 'text', b:[1,0], f: function(){ this.f = this.b; }};
var g = {a: 'text', b:[1,0], f: function(){ this.f = this.b; }};
var h = {a: 'text', b:[1,0], f: function(){ this.a = this.b; }};
var i = {
a: 'text',
c: {
b: [1, 0],
f: function(){
this.a = this.b;
}
}
};
var j = {
a: 'text',
c: {
b: [1, 0],
f: function(){
this.a = this.b;
}
}
};
var k = {a: 'text', b: null};
var l = {a: 'text', b: undefined};
assertTrue(a.equals(b));
assertFalse(a.equals(c));
assertFalse(c.equals(d));
assertFalse(a.equals(e));
assertTrue(f.equals(g));
assertFalse(h.equals(g));
assertTrue(i.equals(j));
assertFalse(d.equals(k));
assertFalse(k.equals(l));

If you work without the JSON library, maybe this will help you out:
Object.prototype.equals = function(b) {
var a = this;
for(i in a) {
if(typeof b[i] == 'undefined') {
return false;
}
if(typeof b[i] == 'object') {
if(!b[i].equals(a[i])) {
return false;
}
}
if(b[i] != a[i]) {
return false;
}
}
for(i in b) {
if(typeof a[i] == 'undefined') {
return false;
}
if(typeof a[i] == 'object') {
if(!a[i].equals(b[i])) {
return false;
}
}
if(a[i] != b[i]) {
return false;
}
}
return true;
}
var a = {foo:'bar', bar: {blub:'bla'}};
var b = {foo:'bar', bar: {blub:'blob'}};
alert(a.equals(b)); // alert's a false

if you want to check for methods explicitly you can use the method.toSource() or method.toString() methods.

back to back or gates with object comparisons. Confusion

To put it simply, i do not understand why they second if statement did not return false for the example (null, null)
function deepEqual(a, b) {
if (a === b) return true;
if (a == null || typeof a != "object" ||
b == null || typeof b != "object")
return false;
var propsInA = 0, propsInB = 0;
for (var prop in a)
propsInA += 1;
for (var prop in b) {
propsInB += 1;
if (!(prop in a) || !deepEqual(a[prop], b[prop]))
return false;
}
return propsInA == propsInB;
}
var obj = {here: {is: "an"}, object: 2};
console.log(deepEqual(obj, obj));
// → true
console.log(deepEqual(obj, {here: 1, object: 2}));
// → false
console.log(deepEqual(obj, {here: {is: "an"}, object: 2}));
// → true

If your code execute return, the next code will not being executed..

Using an ECMA with a null value will always return true.
So - your function will never return false when you pass it a null value - beacuse it will always meet the first if condition , a === b, and return true;. The return statement stops its execution, and will never reach the 2nd if condition.

Swap your if statements. because return will exit the function and null=== null so it will execute the first loop and will not go to the next loop
function deepEqual(a, b) {
if (a == null || typeof a != "object" ||
b == null || typeof b != "object") {
return false;
}
if (a === b) {
return true;
}
}
var c = null;
console.log(deepEqual(c, c));

Because you are returning .before the second statement execute
function deepEqual(a, b) {
if (a === b) {
//return true;
}
if (a == null || typeof a != "object" ||
b == null || typeof b != "object") {
return false;
}
}
var c = null;
console.log(deepEqual(c, c));

Comes from the definition of ===.
As referenced in the Mozilla docs this actually boils down to the definition from Ecma for ===, where it is stated for x === y:
...
1. If Type(x) is different from Type(y), return false.
...
3. If Type(x) is Null, return true.
...
If you call your function with (null, null), then:
Type(x) and Type(y) are the same
Type(x) is Null
∴ null === null ⇒ true

Because first statement is true and it return from here. After return next line code is not executed.
function deepEqual(a, b) {
if (a === b) {
//return true;
}
if (a == null || typeof a != "object" ||
b == null || typeof b != "object") {
return false;
}
}
var c = null;
console.log(deepEqual(c, c));

As others have mentioned, your functions exits out at the first if statement ergo returning false.
if (a === b) {
return true;
}
It is also generally considered good practice to have a single return statement within your functions. In our case, we could refactor our code to something like this:
function deepEqual(a, b) {
var ret = false;
if (a === b) {
ret = true;
} else if (a == null || typeof a != "object" ||
b == null || typeof b != "object") {
ret = false;
}
return ret;
}
This also caters for another possible problem. There are values of a and b that would not have been caught by either if statements and would have returned undefined. e.g:
deepEqual([], {});

Filter duplicate object in array [duplicate]

This question already has answers here:
How to determine equality for two JavaScript objects?
(82 answers)
Closed 6 years ago.
What is the best way to compare objects in JavaScript?
Example:
var user1 = {name : "nerd", org: "dev"};
var user2 = {name : "nerd", org: "dev"};
var eq = user1 == user2;
alert(eq); // gives false
I know that two objects are equal if they refer to the exact same object, but is there a way to check if they have the same attributes' values?
The following way works for me, but is it the only possibility?
var eq = Object.toJSON(user1) == Object.toJSON(user2);
alert(eq); // gives true

Unfortunately there is no perfect way, unless you use _proto_ recursively and access all non-enumerable properties, but this works in Firefox only.
So the best I can do is to guess usage scenarios.
1) Fast and limited.
Works when you have simple JSON-style objects without methods and DOM nodes inside:
JSON.stringify(obj1) === JSON.stringify(obj2)
The ORDER of the properties IS IMPORTANT, so this method will return false for following objects:
x = {a: 1, b: 2};
y = {b: 2, a: 1};
2) Slow and more generic.
Compares objects without digging into prototypes, then compares properties' projections recursively, and also compares constructors.
This is almost correct algorithm:
function deepCompare () {
var i, l, leftChain, rightChain;
function compare2Objects (x, y) {
var p;
// remember that NaN === NaN returns false
// and isNaN(undefined) returns true
if (isNaN(x) && isNaN(y) && typeof x === 'number' && typeof y === 'number') {
return true;
}
// Compare primitives and functions.
// Check if both arguments link to the same object.
// Especially useful on the step where we compare prototypes
if (x === y) {
return true;
}
// Works in case when functions are created in constructor.
// Comparing dates is a common scenario. Another built-ins?
// We can even handle functions passed across iframes
if ((typeof x === 'function' && typeof y === 'function') ||
(x instanceof Date && y instanceof Date) ||
(x instanceof RegExp && y instanceof RegExp) ||
(x instanceof String && y instanceof String) ||
(x instanceof Number && y instanceof Number)) {
return x.toString() === y.toString();
}
// At last checking prototypes as good as we can
if (!(x instanceof Object && y instanceof Object)) {
return false;
}
if (x.isPrototypeOf(y) || y.isPrototypeOf(x)) {
return false;
}
if (x.constructor !== y.constructor) {
return false;
}
if (x.prototype !== y.prototype) {
return false;
}
// Check for infinitive linking loops
if (leftChain.indexOf(x) > -1 || rightChain.indexOf(y) > -1) {
return false;
}
// Quick checking of one object being a subset of another.
// todo: cache the structure of arguments[0] for performance
for (p in y) {
if (y.hasOwnProperty(p) !== x.hasOwnProperty(p)) {
return false;
}
else if (typeof y[p] !== typeof x[p]) {
return false;
}
}
for (p in x) {
if (y.hasOwnProperty(p) !== x.hasOwnProperty(p)) {
return false;
}
else if (typeof y[p] !== typeof x[p]) {
return false;
}
switch (typeof (x[p])) {
case 'object':
case 'function':
leftChain.push(x);
rightChain.push(y);
if (!compare2Objects (x[p], y[p])) {
return false;
}
leftChain.pop();
rightChain.pop();
break;
default:
if (x[p] !== y[p]) {
return false;
}
break;
}
}
return true;
}
if (arguments.length < 1) {
return true; //Die silently? Don't know how to handle such case, please help...
// throw "Need two or more arguments to compare";
}
for (i = 1, l = arguments.length; i < l; i++) {
leftChain = []; //Todo: this can be cached
rightChain = [];
if (!compare2Objects(arguments[0], arguments[i])) {
return false;
}
}
return true;
}
Known issues (well, they have very low priority, probably you'll never notice them):
objects with different prototype structure but same projection
functions may have identical text but refer to different closures
Tests: passes tests are from How to determine equality for two JavaScript objects?.

Here is my ES3 commented solution (gory details after the code):
function object_equals( x, y ) {
if ( x === y ) return true;
// if both x and y are null or undefined and exactly the same
if ( ! ( x instanceof Object ) || ! ( y instanceof Object ) ) return false;
// if they are not strictly equal, they both need to be Objects
if ( x.constructor !== y.constructor ) return false;
// they must have the exact same prototype chain, the closest we can do is
// test there constructor.
for ( var p in x ) {
if ( ! x.hasOwnProperty( p ) ) continue;
// other properties were tested using x.constructor === y.constructor
if ( ! y.hasOwnProperty( p ) ) return false;
// allows to compare x[ p ] and y[ p ] when set to undefined
if ( x[ p ] === y[ p ] ) continue;
// if they have the same strict value or identity then they are equal
if ( typeof( x[ p ] ) !== "object" ) return false;
// Numbers, Strings, Functions, Booleans must be strictly equal
if ( ! object_equals( x[ p ], y[ p ] ) ) return false;
// Objects and Arrays must be tested recursively
}
for ( p in y )
if ( y.hasOwnProperty( p ) && ! x.hasOwnProperty( p ) )
return false;
// allows x[ p ] to be set to undefined
return true;
}
In developing this solution, I took a particular look at corner cases, efficiency, yet trying to yield a simple solution that works, hopefully with some elegance. JavaScript allows both null and undefined properties and objects have prototypes chains that can lead to very different behaviors if not checked.
First I have chosen to not extend Object.prototype, mostly because null could not be one of the objects of the comparison and that I believe that null should be a valid object to compare with another. There are also other legitimate concerns noted by others regarding the extension of Object.prototype regarding possible side effects on other's code.
Special care must taken to deal the possibility that JavaScript allows object properties can be set to undefined, i.e. there exists properties which values are set to undefined. The above solution verifies that both objects have the same properties set to undefined to report equality. This can only be accomplished by checking the existence of properties using Object.hasOwnProperty( property_name ). Also note that JSON.stringify() removes properties that are set to undefined, and that therefore comparisons using this form will ignore properties set to the value undefined.
Functions should be considered equal only if they share the same reference, not just the same code, because this would not take into account these functions prototype. So comparing the code string does not work to guaranty that they have the same prototype object.
The two objects should have the same prototype chain, not just the same properties. This can only be tested cross-browser by comparing the constructor of both objects for strict equality. ECMAScript 5 would allow to test their actual prototype using Object.getPrototypeOf(). Some web browsers also offer a __proto__ property that does the same thing. A possible improvement of the above code would allow to use one of these methods whenever available.
The use of strict comparisons is paramount here because 2 should not be considered equal to "2.0000", nor false should be considered equal to null, undefined, or 0.
Efficiency considerations lead me to compare for equality of properties as soon as possible. Then, only if that failed, look for the typeof these properties. The speed boost could be significant on large objects with lots of scalar properties.
No more that two loops are required, the first to check properties from the left object, the second to check properties from the right and verify only existence (not value), to catch these properties which are defined with the undefined value.
Overall this code handles most corner cases in only 16 lines of code (without comments).
Update (8/13/2015). I have implemented a better version, as the function value_equals() that is faster, handles properly corner cases such as NaN and 0 different than -0, optionally enforcing objects' properties order and testing for cyclic references, backed by more than 100 automated tests as part of the Toubkal project test suite.

Utils.compareObjects = function(o1, o2){
for(var p in o1){
if(o1.hasOwnProperty(p)){
if(o1[p] !== o2[p]){
return false;
}
}
}
for(var p in o2){
if(o2.hasOwnProperty(p)){
if(o1[p] !== o2[p]){
return false;
}
}
}
return true;
};
Simple way to compare ONE-LEVEL only objects.

Certainly not the only way - you could prototype a method (against Object here but I certainly wouldn't suggest using Object for live code) to replicate C#/Java style comparison methods.
Edit, since a general example seems to be expected:
Object.prototype.equals = function(x)
{
for(p in this)
{
switch(typeof(this[p]))
{
case 'object':
if (!this[p].equals(x[p])) { return false }; break;
case 'function':
if (typeof(x[p])=='undefined' || (p != 'equals' && this[p].toString() != x[p].toString())) { return false; }; break;
default:
if (this[p] != x[p]) { return false; }
}
}
for(p in x)
{
if(typeof(this[p])=='undefined') {return false;}
}
return true;
}
Note that testing methods with toString() is absolutely not good enough but a method which would be acceptable is very hard because of the problem of whitespace having meaning or not, never mind synonym methods and methods producing the same result with different implementations. And the problems of prototyping against Object in general.

The following algorithm will deal with self-referential data structures, numbers, strings, dates, and of course plain nested javascript objects:
Objects are considered equivalent when
They are exactly equal per === (String and Number are unwrapped first to ensure 42 is equivalent to Number(42))
or they are both dates and have the same valueOf()
or they are both of the same type and not null and...
they are not objects and are equal per == (catches numbers/strings/booleans)
or, ignoring properties with undefined value they have the same properties all of which are considered recursively equivalent.
Functions are not considered identical by function text. This test is insufficient because functions may have differing closures. Functions are only considered equal if === says so (but you could easily extend that equivalent relation should you choose to do so).
Infinite loops, potentially caused by circular datastructures, are avoided. When areEquivalent attempts to disprove equality and recurses into an object's properties to do so, it keeps track of the objects for which this sub-comparison is needed. If equality can be disproved, then some reachable property path differs between the objects, and then there must be a shortest such reachable path, and that shortest reachable path cannot contain cycles present in both paths; i.e. it is OK to assume equality when recursively comparing objects. The assumption is stored in a property areEquivalent_Eq_91_2_34, which is deleted after use, but if the object graph already contains such a property, behavior is undefined. The use of such a marker property is necessary because javascript doesn't support dictionaries using arbitrary objects as keys.
function unwrapStringOrNumber(obj) {
return (obj instanceof Number || obj instanceof String
? obj.valueOf()
: obj);
}
function areEquivalent(a, b) {
a = unwrapStringOrNumber(a);
b = unwrapStringOrNumber(b);
if (a === b) return true; //e.g. a and b both null
if (a === null || b === null || typeof (a) !== typeof (b)) return false;
if (a instanceof Date)
return b instanceof Date && a.valueOf() === b.valueOf();
if (typeof (a) !== "object")
return a == b; //for boolean, number, string, xml
var newA = (a.areEquivalent_Eq_91_2_34 === undefined),
newB = (b.areEquivalent_Eq_91_2_34 === undefined);
try {
if (newA) a.areEquivalent_Eq_91_2_34 = [];
else if (a.areEquivalent_Eq_91_2_34.some(
function (other) { return other === b; })) return true;
if (newB) b.areEquivalent_Eq_91_2_34 = [];
else if (b.areEquivalent_Eq_91_2_34.some(
function (other) { return other === a; })) return true;
a.areEquivalent_Eq_91_2_34.push(b);
b.areEquivalent_Eq_91_2_34.push(a);
var tmp = {};
for (var prop in a)
if(prop != "areEquivalent_Eq_91_2_34")
tmp[prop] = null;
for (var prop in b)
if (prop != "areEquivalent_Eq_91_2_34")
tmp[prop] = null;
for (var prop in tmp)
if (!areEquivalent(a[prop], b[prop]))
return false;
return true;
} finally {
if (newA) delete a.areEquivalent_Eq_91_2_34;
if (newB) delete b.areEquivalent_Eq_91_2_34;
}
}

I wrote this piece of code for object comparison, and it seems to work. check the assertions:
function countProps(obj) {
var count = 0;
for (k in obj) {
if (obj.hasOwnProperty(k)) {
count++;
}
}
return count;
};
function objectEquals(v1, v2) {
if (typeof(v1) !== typeof(v2)) {
return false;
}
if (typeof(v1) === "function") {
return v1.toString() === v2.toString();
}
if (v1 instanceof Object && v2 instanceof Object) {
if (countProps(v1) !== countProps(v2)) {
return false;
}
var r = true;
for (k in v1) {
r = objectEquals(v1[k], v2[k]);
if (!r) {
return false;
}
}
return true;
} else {
return v1 === v2;
}
}
assert.isTrue(objectEquals(null,null));
assert.isFalse(objectEquals(null,undefined));
assert.isTrue(objectEquals("hi","hi"));
assert.isTrue(objectEquals(5,5));
assert.isFalse(objectEquals(5,10));
assert.isTrue(objectEquals([],[]));
assert.isTrue(objectEquals([1,2],[1,2]));
assert.isFalse(objectEquals([1,2],[2,1]));
assert.isFalse(objectEquals([1,2],[1,2,3]));
assert.isTrue(objectEquals({},{}));
assert.isTrue(objectEquals({a:1,b:2},{a:1,b:2}));
assert.isTrue(objectEquals({a:1,b:2},{b:2,a:1}));
assert.isFalse(objectEquals({a:1,b:2},{a:1,b:3}));
assert.isTrue(objectEquals({1:{name:"mhc",age:28}, 2:{name:"arb",age:26}},{1:{name:"mhc",age:28}, 2:{name:"arb",age:26}}));
assert.isFalse(objectEquals({1:{name:"mhc",age:28}, 2:{name:"arb",age:26}},{1:{name:"mhc",age:28}, 2:{name:"arb",age:27}}));
assert.isTrue(objectEquals(function(x){return x;},function(x){return x;}));
assert.isFalse(objectEquals(function(x){return x;},function(y){return y+2;}));

I have modified a bit the code above. for me 0 !== false and null !== undefined. If you do not need such strict check remove one "=" sign in "this[p] !== x[p]" inside the code.
Object.prototype.equals = function(x){
for (var p in this) {
if(typeof(this[p]) !== typeof(x[p])) return false;
if((this[p]===null) !== (x[p]===null)) return false;
switch (typeof(this[p])) {
case 'undefined':
if (typeof(x[p]) != 'undefined') return false;
break;
case 'object':
if(this[p]!==null && x[p]!==null && (this[p].constructor.toString() !== x[p].constructor.toString() || !this[p].equals(x[p]))) return false;
break;
case 'function':
if (p != 'equals' && this[p].toString() != x[p].toString()) return false;
break;
default:
if (this[p] !== x[p]) return false;
}
}
return true;
}
Then I have tested it with next objects:
var a = {a: 'text', b:[0,1]};
var b = {a: 'text', b:[0,1]};
var c = {a: 'text', b: 0};
var d = {a: 'text', b: false};
var e = {a: 'text', b:[1,0]};
var f = {a: 'text', b:[1,0], f: function(){ this.f = this.b; }};
var g = {a: 'text', b:[1,0], f: function(){ this.f = this.b; }};
var h = {a: 'text', b:[1,0], f: function(){ this.a = this.b; }};
var i = {
a: 'text',
c: {
b: [1, 0],
f: function(){
this.a = this.b;
}
}
};
var j = {
a: 'text',
c: {
b: [1, 0],
f: function(){
this.a = this.b;
}
}
};
var k = {a: 'text', b: null};
var l = {a: 'text', b: undefined};
a==b expected true; returned true
a==c expected false; returned false
c==d expected false; returned false
a==e expected false; returned false
f==g expected true; returned true
h==g expected false; returned false
i==j expected true; returned true
d==k expected false; returned false
k==l expected false; returned false

Here is my version, pretty much stuff from this thread is integrated (same counts for the test cases):
Object.defineProperty(Object.prototype, "equals", {
enumerable: false,
value: function (obj) {
var p;
if (this === obj) {
return true;
}
// some checks for native types first
// function and sring
if (typeof(this) === "function" || typeof(this) === "string" || this instanceof String) {
return this.toString() === obj.toString();
}
// number
if (this instanceof Number || typeof(this) === "number") {
if (obj instanceof Number || typeof(obj) === "number") {
return this.valueOf() === obj.valueOf();
}
return false;
}
// null.equals(null) and undefined.equals(undefined) do not inherit from the
// Object.prototype so we can return false when they are passed as obj
if (typeof(this) !== typeof(obj) || obj === null || typeof(obj) === "undefined") {
return false;
}
function sort (o) {
var result = {};
if (typeof o !== "object") {
return o;
}
Object.keys(o).sort().forEach(function (key) {
result[key] = sort(o[key]);
});
return result;
}
if (typeof(this) === "object") {
if (Array.isArray(this)) { // check on arrays
return JSON.stringify(this) === JSON.stringify(obj);
} else { // anyway objects
for (p in this) {
if (typeof(this[p]) !== typeof(obj[p])) {
return false;
}
if ((this[p] === null) !== (obj[p] === null)) {
return false;
}
switch (typeof(this[p])) {
case 'undefined':
if (typeof(obj[p]) !== 'undefined') {
return false;
}
break;
case 'object':
if (this[p] !== null
&& obj[p] !== null
&& (this[p].constructor.toString() !== obj[p].constructor.toString()
|| !this[p].equals(obj[p]))) {
return false;
}
break;
case 'function':
if (this[p].toString() !== obj[p].toString()) {
return false;
}
break;
default:
if (this[p] !== obj[p]) {
return false;
}
}
};
}
}
// at least check them with JSON
return JSON.stringify(sort(this)) === JSON.stringify(sort(obj));
}
});
Here is my TestCase:
assertFalse({}.equals(null));
assertFalse({}.equals(undefined));
assertTrue("String", "hi".equals("hi"));
assertTrue("Number", new Number(5).equals(5));
assertFalse("Number", new Number(5).equals(10));
assertFalse("Number+String", new Number(1).equals("1"));
assertTrue([].equals([]));
assertTrue([1,2].equals([1,2]));
assertFalse([1,2].equals([2,1]));
assertFalse([1,2].equals([1,2,3]));
assertTrue(new Date("2011-03-31").equals(new Date("2011-03-31")));
assertFalse(new Date("2011-03-31").equals(new Date("1970-01-01")));
assertTrue({}.equals({}));
assertTrue({a:1,b:2}.equals({a:1,b:2}));
assertTrue({a:1,b:2}.equals({b:2,a:1}));
assertFalse({a:1,b:2}.equals({a:1,b:3}));
assertTrue({1:{name:"mhc",age:28}, 2:{name:"arb",age:26}}.equals({1:{name:"mhc",age:28}, 2:{name:"arb",age:26}}));
assertFalse({1:{name:"mhc",age:28}, 2:{name:"arb",age:26}}.equals({1:{name:"mhc",age:28}, 2:{name:"arb",age:27}}));
assertTrue("Function", (function(x){return x;}).equals(function(x){return x;}));
assertFalse("Function", (function(x){return x;}).equals(function(y){return y+2;}));
var a = {a: 'text', b:[0,1]};
var b = {a: 'text', b:[0,1]};
var c = {a: 'text', b: 0};
var d = {a: 'text', b: false};
var e = {a: 'text', b:[1,0]};
var f = {a: 'text', b:[1,0], f: function(){ this.f = this.b; }};
var g = {a: 'text', b:[1,0], f: function(){ this.f = this.b; }};
var h = {a: 'text', b:[1,0], f: function(){ this.a = this.b; }};
var i = {
a: 'text',
c: {
b: [1, 0],
f: function(){
this.a = this.b;
}
}
};
var j = {
a: 'text',
c: {
b: [1, 0],
f: function(){
this.a = this.b;
}
}
};
var k = {a: 'text', b: null};
var l = {a: 'text', b: undefined};
assertTrue(a.equals(b));
assertFalse(a.equals(c));
assertFalse(c.equals(d));
assertFalse(a.equals(e));
assertTrue(f.equals(g));
assertFalse(h.equals(g));
assertTrue(i.equals(j));
assertFalse(d.equals(k));
assertFalse(k.equals(l));

If you work without the JSON library, maybe this will help you out:
Object.prototype.equals = function(b) {
var a = this;
for(i in a) {
if(typeof b[i] == 'undefined') {
return false;
}
if(typeof b[i] == 'object') {
if(!b[i].equals(a[i])) {
return false;
}
}
if(b[i] != a[i]) {
return false;
}
}
for(i in b) {
if(typeof a[i] == 'undefined') {
return false;
}
if(typeof a[i] == 'object') {
if(!a[i].equals(b[i])) {
return false;
}
}
if(a[i] != b[i]) {
return false;
}
}
return true;
}
var a = {foo:'bar', bar: {blub:'bla'}};
var b = {foo:'bar', bar: {blub:'blob'}};
alert(a.equals(b)); // alert's a false

if you want to check for methods explicitly you can use the method.toSource() or method.toString() methods.

Javascript If statement - should be true, evaluating to false [duplicate]

This question already has answers here:
How to determine equality for two JavaScript objects?
(82 answers)
Closed 6 years ago.
What is the best way to compare objects in JavaScript?
Example:
var user1 = {name : "nerd", org: "dev"};
var user2 = {name : "nerd", org: "dev"};
var eq = user1 == user2;
alert(eq); // gives false
I know that two objects are equal if they refer to the exact same object, but is there a way to check if they have the same attributes' values?
The following way works for me, but is it the only possibility?
var eq = Object.toJSON(user1) == Object.toJSON(user2);
alert(eq); // gives true

Unfortunately there is no perfect way, unless you use _proto_ recursively and access all non-enumerable properties, but this works in Firefox only.
So the best I can do is to guess usage scenarios.
1) Fast and limited.
Works when you have simple JSON-style objects without methods and DOM nodes inside:
JSON.stringify(obj1) === JSON.stringify(obj2)
The ORDER of the properties IS IMPORTANT, so this method will return false for following objects:
x = {a: 1, b: 2};
y = {b: 2, a: 1};
2) Slow and more generic.
Compares objects without digging into prototypes, then compares properties' projections recursively, and also compares constructors.
This is almost correct algorithm:
function deepCompare () {
var i, l, leftChain, rightChain;
function compare2Objects (x, y) {
var p;
// remember that NaN === NaN returns false
// and isNaN(undefined) returns true
if (isNaN(x) && isNaN(y) && typeof x === 'number' && typeof y === 'number') {
return true;
}
// Compare primitives and functions.
// Check if both arguments link to the same object.
// Especially useful on the step where we compare prototypes
if (x === y) {
return true;
}
// Works in case when functions are created in constructor.
// Comparing dates is a common scenario. Another built-ins?
// We can even handle functions passed across iframes
if ((typeof x === 'function' && typeof y === 'function') ||
(x instanceof Date && y instanceof Date) ||
(x instanceof RegExp && y instanceof RegExp) ||
(x instanceof String && y instanceof String) ||
(x instanceof Number && y instanceof Number)) {
return x.toString() === y.toString();
}
// At last checking prototypes as good as we can
if (!(x instanceof Object && y instanceof Object)) {
return false;
}
if (x.isPrototypeOf(y) || y.isPrototypeOf(x)) {
return false;
}
if (x.constructor !== y.constructor) {
return false;
}
if (x.prototype !== y.prototype) {
return false;
}
// Check for infinitive linking loops
if (leftChain.indexOf(x) > -1 || rightChain.indexOf(y) > -1) {
return false;
}
// Quick checking of one object being a subset of another.
// todo: cache the structure of arguments[0] for performance
for (p in y) {
if (y.hasOwnProperty(p) !== x.hasOwnProperty(p)) {
return false;
}
else if (typeof y[p] !== typeof x[p]) {
return false;
}
}
for (p in x) {
if (y.hasOwnProperty(p) !== x.hasOwnProperty(p)) {
return false;
}
else if (typeof y[p] !== typeof x[p]) {
return false;
}
switch (typeof (x[p])) {
case 'object':
case 'function':
leftChain.push(x);
rightChain.push(y);
if (!compare2Objects (x[p], y[p])) {
return false;
}
leftChain.pop();
rightChain.pop();
break;
default:
if (x[p] !== y[p]) {
return false;
}
break;
}
}
return true;
}
if (arguments.length < 1) {
return true; //Die silently? Don't know how to handle such case, please help...
// throw "Need two or more arguments to compare";
}
for (i = 1, l = arguments.length; i < l; i++) {
leftChain = []; //Todo: this can be cached
rightChain = [];
if (!compare2Objects(arguments[0], arguments[i])) {
return false;
}
}
return true;
}
Known issues (well, they have very low priority, probably you'll never notice them):
objects with different prototype structure but same projection
functions may have identical text but refer to different closures
Tests: passes tests are from How to determine equality for two JavaScript objects?.

Here is my ES3 commented solution (gory details after the code):
function object_equals( x, y ) {
if ( x === y ) return true;
// if both x and y are null or undefined and exactly the same
if ( ! ( x instanceof Object ) || ! ( y instanceof Object ) ) return false;
// if they are not strictly equal, they both need to be Objects
if ( x.constructor !== y.constructor ) return false;
// they must have the exact same prototype chain, the closest we can do is
// test there constructor.
for ( var p in x ) {
if ( ! x.hasOwnProperty( p ) ) continue;
// other properties were tested using x.constructor === y.constructor
if ( ! y.hasOwnProperty( p ) ) return false;
// allows to compare x[ p ] and y[ p ] when set to undefined
if ( x[ p ] === y[ p ] ) continue;
// if they have the same strict value or identity then they are equal
if ( typeof( x[ p ] ) !== "object" ) return false;
// Numbers, Strings, Functions, Booleans must be strictly equal
if ( ! object_equals( x[ p ], y[ p ] ) ) return false;
// Objects and Arrays must be tested recursively
}
for ( p in y )
if ( y.hasOwnProperty( p ) && ! x.hasOwnProperty( p ) )
return false;
// allows x[ p ] to be set to undefined
return true;
}
In developing this solution, I took a particular look at corner cases, efficiency, yet trying to yield a simple solution that works, hopefully with some elegance. JavaScript allows both null and undefined properties and objects have prototypes chains that can lead to very different behaviors if not checked.
First I have chosen to not extend Object.prototype, mostly because null could not be one of the objects of the comparison and that I believe that null should be a valid object to compare with another. There are also other legitimate concerns noted by others regarding the extension of Object.prototype regarding possible side effects on other's code.
Special care must taken to deal the possibility that JavaScript allows object properties can be set to undefined, i.e. there exists properties which values are set to undefined. The above solution verifies that both objects have the same properties set to undefined to report equality. This can only be accomplished by checking the existence of properties using Object.hasOwnProperty( property_name ). Also note that JSON.stringify() removes properties that are set to undefined, and that therefore comparisons using this form will ignore properties set to the value undefined.
Functions should be considered equal only if they share the same reference, not just the same code, because this would not take into account these functions prototype. So comparing the code string does not work to guaranty that they have the same prototype object.
The two objects should have the same prototype chain, not just the same properties. This can only be tested cross-browser by comparing the constructor of both objects for strict equality. ECMAScript 5 would allow to test their actual prototype using Object.getPrototypeOf(). Some web browsers also offer a __proto__ property that does the same thing. A possible improvement of the above code would allow to use one of these methods whenever available.
The use of strict comparisons is paramount here because 2 should not be considered equal to "2.0000", nor false should be considered equal to null, undefined, or 0.
Efficiency considerations lead me to compare for equality of properties as soon as possible. Then, only if that failed, look for the typeof these properties. The speed boost could be significant on large objects with lots of scalar properties.
No more that two loops are required, the first to check properties from the left object, the second to check properties from the right and verify only existence (not value), to catch these properties which are defined with the undefined value.
Overall this code handles most corner cases in only 16 lines of code (without comments).
Update (8/13/2015). I have implemented a better version, as the function value_equals() that is faster, handles properly corner cases such as NaN and 0 different than -0, optionally enforcing objects' properties order and testing for cyclic references, backed by more than 100 automated tests as part of the Toubkal project test suite.

Utils.compareObjects = function(o1, o2){
for(var p in o1){
if(o1.hasOwnProperty(p)){
if(o1[p] !== o2[p]){
return false;
}
}
}
for(var p in o2){
if(o2.hasOwnProperty(p)){
if(o1[p] !== o2[p]){
return false;
}
}
}
return true;
};
Simple way to compare ONE-LEVEL only objects.

Certainly not the only way - you could prototype a method (against Object here but I certainly wouldn't suggest using Object for live code) to replicate C#/Java style comparison methods.
Edit, since a general example seems to be expected:
Object.prototype.equals = function(x)
{
for(p in this)
{
switch(typeof(this[p]))
{
case 'object':
if (!this[p].equals(x[p])) { return false }; break;
case 'function':
if (typeof(x[p])=='undefined' || (p != 'equals' && this[p].toString() != x[p].toString())) { return false; }; break;
default:
if (this[p] != x[p]) { return false; }
}
}
for(p in x)
{
if(typeof(this[p])=='undefined') {return false;}
}
return true;
}
Note that testing methods with toString() is absolutely not good enough but a method which would be acceptable is very hard because of the problem of whitespace having meaning or not, never mind synonym methods and methods producing the same result with different implementations. And the problems of prototyping against Object in general.

The following algorithm will deal with self-referential data structures, numbers, strings, dates, and of course plain nested javascript objects:
Objects are considered equivalent when
They are exactly equal per === (String and Number are unwrapped first to ensure 42 is equivalent to Number(42))
or they are both dates and have the same valueOf()
or they are both of the same type and not null and...
they are not objects and are equal per == (catches numbers/strings/booleans)
or, ignoring properties with undefined value they have the same properties all of which are considered recursively equivalent.
Functions are not considered identical by function text. This test is insufficient because functions may have differing closures. Functions are only considered equal if === says so (but you could easily extend that equivalent relation should you choose to do so).
Infinite loops, potentially caused by circular datastructures, are avoided. When areEquivalent attempts to disprove equality and recurses into an object's properties to do so, it keeps track of the objects for which this sub-comparison is needed. If equality can be disproved, then some reachable property path differs between the objects, and then there must be a shortest such reachable path, and that shortest reachable path cannot contain cycles present in both paths; i.e. it is OK to assume equality when recursively comparing objects. The assumption is stored in a property areEquivalent_Eq_91_2_34, which is deleted after use, but if the object graph already contains such a property, behavior is undefined. The use of such a marker property is necessary because javascript doesn't support dictionaries using arbitrary objects as keys.
function unwrapStringOrNumber(obj) {
return (obj instanceof Number || obj instanceof String
? obj.valueOf()
: obj);
}
function areEquivalent(a, b) {
a = unwrapStringOrNumber(a);
b = unwrapStringOrNumber(b);
if (a === b) return true; //e.g. a and b both null
if (a === null || b === null || typeof (a) !== typeof (b)) return false;
if (a instanceof Date)
return b instanceof Date && a.valueOf() === b.valueOf();
if (typeof (a) !== "object")
return a == b; //for boolean, number, string, xml
var newA = (a.areEquivalent_Eq_91_2_34 === undefined),
newB = (b.areEquivalent_Eq_91_2_34 === undefined);
try {
if (newA) a.areEquivalent_Eq_91_2_34 = [];
else if (a.areEquivalent_Eq_91_2_34.some(
function (other) { return other === b; })) return true;
if (newB) b.areEquivalent_Eq_91_2_34 = [];
else if (b.areEquivalent_Eq_91_2_34.some(
function (other) { return other === a; })) return true;
a.areEquivalent_Eq_91_2_34.push(b);
b.areEquivalent_Eq_91_2_34.push(a);
var tmp = {};
for (var prop in a)
if(prop != "areEquivalent_Eq_91_2_34")
tmp[prop] = null;
for (var prop in b)
if (prop != "areEquivalent_Eq_91_2_34")
tmp[prop] = null;
for (var prop in tmp)
if (!areEquivalent(a[prop], b[prop]))
return false;
return true;
} finally {
if (newA) delete a.areEquivalent_Eq_91_2_34;
if (newB) delete b.areEquivalent_Eq_91_2_34;
}
}

I wrote this piece of code for object comparison, and it seems to work. check the assertions:
function countProps(obj) {
var count = 0;
for (k in obj) {
if (obj.hasOwnProperty(k)) {
count++;
}
}
return count;
};
function objectEquals(v1, v2) {
if (typeof(v1) !== typeof(v2)) {
return false;
}
if (typeof(v1) === "function") {
return v1.toString() === v2.toString();
}
if (v1 instanceof Object && v2 instanceof Object) {
if (countProps(v1) !== countProps(v2)) {
return false;
}
var r = true;
for (k in v1) {
r = objectEquals(v1[k], v2[k]);
if (!r) {
return false;
}
}
return true;
} else {
return v1 === v2;
}
}
assert.isTrue(objectEquals(null,null));
assert.isFalse(objectEquals(null,undefined));
assert.isTrue(objectEquals("hi","hi"));
assert.isTrue(objectEquals(5,5));
assert.isFalse(objectEquals(5,10));
assert.isTrue(objectEquals([],[]));
assert.isTrue(objectEquals([1,2],[1,2]));
assert.isFalse(objectEquals([1,2],[2,1]));
assert.isFalse(objectEquals([1,2],[1,2,3]));
assert.isTrue(objectEquals({},{}));
assert.isTrue(objectEquals({a:1,b:2},{a:1,b:2}));
assert.isTrue(objectEquals({a:1,b:2},{b:2,a:1}));
assert.isFalse(objectEquals({a:1,b:2},{a:1,b:3}));
assert.isTrue(objectEquals({1:{name:"mhc",age:28}, 2:{name:"arb",age:26}},{1:{name:"mhc",age:28}, 2:{name:"arb",age:26}}));
assert.isFalse(objectEquals({1:{name:"mhc",age:28}, 2:{name:"arb",age:26}},{1:{name:"mhc",age:28}, 2:{name:"arb",age:27}}));
assert.isTrue(objectEquals(function(x){return x;},function(x){return x;}));
assert.isFalse(objectEquals(function(x){return x;},function(y){return y+2;}));

I have modified a bit the code above. for me 0 !== false and null !== undefined. If you do not need such strict check remove one "=" sign in "this[p] !== x[p]" inside the code.
Object.prototype.equals = function(x){
for (var p in this) {
if(typeof(this[p]) !== typeof(x[p])) return false;
if((this[p]===null) !== (x[p]===null)) return false;
switch (typeof(this[p])) {
case 'undefined':
if (typeof(x[p]) != 'undefined') return false;
break;
case 'object':
if(this[p]!==null && x[p]!==null && (this[p].constructor.toString() !== x[p].constructor.toString() || !this[p].equals(x[p]))) return false;
break;
case 'function':
if (p != 'equals' && this[p].toString() != x[p].toString()) return false;
break;
default:
if (this[p] !== x[p]) return false;
}
}
return true;
}
Then I have tested it with next objects:
var a = {a: 'text', b:[0,1]};
var b = {a: 'text', b:[0,1]};
var c = {a: 'text', b: 0};
var d = {a: 'text', b: false};
var e = {a: 'text', b:[1,0]};
var f = {a: 'text', b:[1,0], f: function(){ this.f = this.b; }};
var g = {a: 'text', b:[1,0], f: function(){ this.f = this.b; }};
var h = {a: 'text', b:[1,0], f: function(){ this.a = this.b; }};
var i = {
a: 'text',
c: {
b: [1, 0],
f: function(){
this.a = this.b;
}
}
};
var j = {
a: 'text',
c: {
b: [1, 0],
f: function(){
this.a = this.b;
}
}
};
var k = {a: 'text', b: null};
var l = {a: 'text', b: undefined};
a==b expected true; returned true
a==c expected false; returned false
c==d expected false; returned false
a==e expected false; returned false
f==g expected true; returned true
h==g expected false; returned false
i==j expected true; returned true
d==k expected false; returned false
k==l expected false; returned false

Here is my version, pretty much stuff from this thread is integrated (same counts for the test cases):
Object.defineProperty(Object.prototype, "equals", {
enumerable: false,
value: function (obj) {
var p;
if (this === obj) {
return true;
}
// some checks for native types first
// function and sring
if (typeof(this) === "function" || typeof(this) === "string" || this instanceof String) {
return this.toString() === obj.toString();
}
// number
if (this instanceof Number || typeof(this) === "number") {
if (obj instanceof Number || typeof(obj) === "number") {
return this.valueOf() === obj.valueOf();
}
return false;
}
// null.equals(null) and undefined.equals(undefined) do not inherit from the
// Object.prototype so we can return false when they are passed as obj
if (typeof(this) !== typeof(obj) || obj === null || typeof(obj) === "undefined") {
return false;
}
function sort (o) {
var result = {};
if (typeof o !== "object") {
return o;
}
Object.keys(o).sort().forEach(function (key) {
result[key] = sort(o[key]);
});
return result;
}
if (typeof(this) === "object") {
if (Array.isArray(this)) { // check on arrays
return JSON.stringify(this) === JSON.stringify(obj);
} else { // anyway objects
for (p in this) {
if (typeof(this[p]) !== typeof(obj[p])) {
return false;
}
if ((this[p] === null) !== (obj[p] === null)) {
return false;
}
switch (typeof(this[p])) {
case 'undefined':
if (typeof(obj[p]) !== 'undefined') {
return false;
}
break;
case 'object':
if (this[p] !== null
&& obj[p] !== null
&& (this[p].constructor.toString() !== obj[p].constructor.toString()
|| !this[p].equals(obj[p]))) {
return false;
}
break;
case 'function':
if (this[p].toString() !== obj[p].toString()) {
return false;
}
break;
default:
if (this[p] !== obj[p]) {
return false;
}
}
};
}
}
// at least check them with JSON
return JSON.stringify(sort(this)) === JSON.stringify(sort(obj));
}
});
Here is my TestCase:
assertFalse({}.equals(null));
assertFalse({}.equals(undefined));
assertTrue("String", "hi".equals("hi"));
assertTrue("Number", new Number(5).equals(5));
assertFalse("Number", new Number(5).equals(10));
assertFalse("Number+String", new Number(1).equals("1"));
assertTrue([].equals([]));
assertTrue([1,2].equals([1,2]));
assertFalse([1,2].equals([2,1]));
assertFalse([1,2].equals([1,2,3]));
assertTrue(new Date("2011-03-31").equals(new Date("2011-03-31")));
assertFalse(new Date("2011-03-31").equals(new Date("1970-01-01")));
assertTrue({}.equals({}));
assertTrue({a:1,b:2}.equals({a:1,b:2}));
assertTrue({a:1,b:2}.equals({b:2,a:1}));
assertFalse({a:1,b:2}.equals({a:1,b:3}));
assertTrue({1:{name:"mhc",age:28}, 2:{name:"arb",age:26}}.equals({1:{name:"mhc",age:28}, 2:{name:"arb",age:26}}));
assertFalse({1:{name:"mhc",age:28}, 2:{name:"arb",age:26}}.equals({1:{name:"mhc",age:28}, 2:{name:"arb",age:27}}));
assertTrue("Function", (function(x){return x;}).equals(function(x){return x;}));
assertFalse("Function", (function(x){return x;}).equals(function(y){return y+2;}));
var a = {a: 'text', b:[0,1]};
var b = {a: 'text', b:[0,1]};
var c = {a: 'text', b: 0};
var d = {a: 'text', b: false};
var e = {a: 'text', b:[1,0]};
var f = {a: 'text', b:[1,0], f: function(){ this.f = this.b; }};
var g = {a: 'text', b:[1,0], f: function(){ this.f = this.b; }};
var h = {a: 'text', b:[1,0], f: function(){ this.a = this.b; }};
var i = {
a: 'text',
c: {
b: [1, 0],
f: function(){
this.a = this.b;
}
}
};
var j = {
a: 'text',
c: {
b: [1, 0],
f: function(){
this.a = this.b;
}
}
};
var k = {a: 'text', b: null};
var l = {a: 'text', b: undefined};
assertTrue(a.equals(b));
assertFalse(a.equals(c));
assertFalse(c.equals(d));
assertFalse(a.equals(e));
assertTrue(f.equals(g));
assertFalse(h.equals(g));
assertTrue(i.equals(j));
assertFalse(d.equals(k));
assertFalse(k.equals(l));

If you work without the JSON library, maybe this will help you out:
Object.prototype.equals = function(b) {
var a = this;
for(i in a) {
if(typeof b[i] == 'undefined') {
return false;
}
if(typeof b[i] == 'object') {
if(!b[i].equals(a[i])) {
return false;
}
}
if(b[i] != a[i]) {
return false;
}
}
for(i in b) {
if(typeof a[i] == 'undefined') {
return false;
}
if(typeof a[i] == 'object') {
if(!a[i].equals(b[i])) {
return false;
}
}
if(a[i] != b[i]) {
return false;
}
}
return true;
}
var a = {foo:'bar', bar: {blub:'bla'}};
var b = {foo:'bar', bar: {blub:'blob'}};
alert(a.equals(b)); // alert's a false

if you want to check for methods explicitly you can use the method.toSource() or method.toString() methods.

Develop Reference

JavaScript is the programming language of the Web.

JavaScript: Deep comparison recursively: Objects and properties - javascript

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