Develop Reference

How to write a Ternary Operator for this operation? [duplicate]

I've got an array:
myArray = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}, etc.]
I'm unable to change the structure of the array. I'm being passed an id of 45, and I want to get 'bar' for that object in the array.
How do I do this in JavaScript or using jQuery?

Use the find() method:
myArray.find(x => x.id === '45').foo;
From MDN:
The find() method returns the first value in the array, if an element in the array satisfies the provided testing function. Otherwise undefined is returned.
If you want to find its index instead, use findIndex():
myArray.findIndex(x => x.id === '45');
From MDN:
The findIndex() method returns the index of the first element in the array that satisfies the provided testing function. Otherwise -1 is returned.
If you want to get an array of matching elements, use the filter() method instead:
myArray.filter(x => x.id === '45');
This will return an array of objects. If you want to get an array of foo properties, you can do this with the map() method:
myArray.filter(x => x.id === '45').map(x => x.foo);
Side note: methods like find() or filter(), and arrow functions are not supported by older browsers (like IE), so if you want to support these browsers, you should transpile your code using Babel (with the polyfill).

As you are already using jQuery, you can use the grep function which is intended for searching an array:
var result = $.grep(myArray, function(e){ return e.id == id; });
The result is an array with the items found. If you know that the object is always there and that it only occurs once, you can just use result[0].foo to get the value. Otherwise you should check the length of the resulting array. Example:
if (result.length === 0) {
// no result found
} else if (result.length === 1) {
// property found, access the foo property using result[0].foo
} else {
// multiple items found
}

Another solution is to create a lookup object:
var lookup = {};
for (var i = 0, len = array.length; i < len; i++) {
lookup[array[i].id] = array[i];
}
... now you can use lookup[id]...
This is especially interesting if you need to do many lookups.
This won't need much more memory since the IDs and objects will be shared.

ECMAScript 2015 (JavaScript ES6) provides the find()
method on arrays:
var myArray = [
{id:1, name:"bob"},
{id:2, name:"dan"},
{id:3, name:"barb"},
]
// grab the Array item which matchs the id "2"
var item = myArray.find(item => item.id === 2);
// print
console.log(item.name);
It works without external libraries. But if you want older browser support you might want to include this polyfill.

Underscore.js has a nice method for that:
myArray = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'},etc.]
obj = _.find(myArray, function(obj) { return obj.id == '45' })

I think the easiest way would be the following, but it won't work on Internet Explorer 8 (or earlier):
var result = myArray.filter(function(v) {
return v.id === '45'; // Filter out the appropriate one
})[0].foo; // Get result and access the foo property

Try the following
function findById(source, id) {
for (var i = 0; i < source.length; i++) {
if (source[i].id === id) {
return source[i];
}
}
throw "Couldn't find object with id: " + id;
}

myArray.filter(function(a){ return a.id == some_id_you_want })[0]

A generic and more flexible version of the findById function above:
// array = [{key:value},{key:value}]
function objectFindByKey(array, key, value) {
for (var i = 0; i < array.length; i++) {
if (array[i][key] === value) {
return array[i];
}
}
return null;
}
var array = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}];
var result_obj = objectFindByKey(array, 'id', '45');

Performance
Today 2020.06.20 I perform test on MacOs High Sierra on Chrome 81.0, Firefox 77.0 and Safari 13.1 for chosen solutions.
Conclusions for solutions which use precalculations
Solutions with precalculations (K,L) are (much much) faster than other solutions and will not be compared with them - probably they are use some special build-in browser optimisations
surprisingly on Chrome and Safari solution based on Map (K) are much faster than solution based on object {} (L)
surprisingly on Safari for small arrays solution based on object {} (L) is slower than traditional for (E)
surprisingly on Firefox for small arrays solution based on Map (K) is slower than traditional for (E)
Conclusions when searched objects ALWAYS exists
solution which use traditional for (E) is fastest for small arrays and fast for big arrays
solution using cache (J) is fastest for big arrays - surprisingly for small arrays is medium fast
solutions based on find (A) and findIndex (B) are fast for small arras and medium fast on big arrays
solution based on $.map (H) is slowest on small arrays
solution based on reduce (D) is slowest on big arrays
Conclusions when searched objects NEVER exists
solution based on traditional for (E) is fastest on small and big arrays (except Chrome-small arrays where it is second fast)
solution based on reduce (D) is slowest on big arrays
solution which use cache (J) is medium fast but can be speed up if we save in cache also keys which have null values (which was not done here because we want to avoid unlimited memory consumption in cache in case when many not existing keys will be searched)
Details
For solutions
without precalculations: A
B
C
D
E
F
G
H
I
J (the J solution use 'inner' cache and it speed depend on how often searched elements will repeat)
with precalculations
K
L
I perform four tests. In tests I want to find 5 objects in 10 loop iterations (the objects ID not change during iterations) - so I call tested method 50 times but only first 5 times have unique id values:
small array (10 elements) and searched object ALWAYS exists - you can perform it HERE
big array (10k elements) and searched object ALWAYS exist - you can perform it HERE
small array (10 elements) and searched object NEVER exists - you can perform it HERE
big array (10k elements) and searched object NEVER exists - you can perform it HERE
Tested codes are presented below
function A(arr, id) {
return arr.find(o=> o.id==id);
}
function B(arr, id) {
let idx= arr.findIndex(o=> o.id==id);
return arr[idx];
}
function C(arr, id) {
return arr.filter(o=> o.id==id)[0];
}
function D(arr, id) {
return arr.reduce((a, b) => (a.id==id && a) || (b.id == id && b));
}
function E(arr, id) {
for (var i = 0; i < arr.length; i++) if (arr[i].id==id) return arr[i];
return null;
}
function F(arr, id) {
var retObj ={};
$.each(arr, (index, obj) => {
if (obj.id == id) {
retObj = obj;
return false;
}
});
return retObj;
}
function G(arr, id) {
return $.grep(arr, e=> e.id == id )[0];
}
function H(arr, id) {
return $.map(myArray, function(val) {
return val.id == id ? val : null;
})[0];
}
function I(arr, id) {
return _.find(arr, o => o.id==id);
}
let J = (()=>{
let cache = new Map();
return function J(arr,id,el=null) {
return cache.get(id) || (el=arr.find(o=> o.id==id), cache.set(id,el), el);
}
})();
function K(arr, id) {
return mapK.get(id)
}
function L(arr, id) {
return mapL[id];
}
// -------------
// TEST
// -------------
console.log('Find id=5');
myArray = [...Array(10)].map((x,i)=> ({'id':`${i}`, 'foo':`bar_${i}`}));
const mapK = new Map( myArray.map(el => [el.id, el]) );
const mapL = {}; myArray.forEach(el => mapL[el.id]=el);
[A,B,C,D,E,F,G,H,I,J,K,L].forEach(f=> console.log(`${f.name}: ${JSON.stringify(f(myArray, '5'))}`));
console.log('Whole array',JSON.stringify(myArray));
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.15/lodash.min.js"></script>
This snippet only presents tested codes
Example tests results for Chrome for small array where searched objects always exists

As others have pointed out, .find() is the way to go when looking for one object within your array. However, if your object cannot be found using this method, your program will crash:
const myArray = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}];
const res = myArray.find(x => x.id === '100').foo; // Uh oh!
/*
Error:
"Uncaught TypeError: Cannot read property 'foo' of undefined"
or in newer chrome versions:
Uncaught TypeError: Cannot read properties of undefined (reading 'foo')
*/
This can be fixed by checking whether the result of .find() is defined before using .foo on it. Modern JS allows us to do this easily with optional chaining, returning undefined if the object cannot be found, rather than crashing your code:
const myArray = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}];
const res = myArray.find(x => x.id === '100')?.foo; // No error!
console.log(res); // undefined when the object cannot be found

If you do this multiple times, you may set up a Map (ES6):
const map = new Map( myArray.map(el => [el.id, el]) );
Then you can simply do a O(1) lookup:
map.get(27).foo

You can get this easily using the map() function:
myArray = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}];
var found = $.map(myArray, function(val) {
return val.id == 45 ? val.foo : null;
});
//found[0] == "bar";
Working example: http://jsfiddle.net/hunter/Pxaua/

Using native Array.reduce
var array = [ {'id':'73' ,'foo':'bar'} , {'id':'45' ,'foo':'bar'} , ];
var id = 73;
var found = array.reduce(function(a, b){
return (a.id==id && a) || (b.id == id && b)
});
returns the object element if found, otherwise false

You can use filters,
function getById(id, myArray) {
return myArray.filter(function(obj) {
if(obj.id == id) {
return obj
}
})[0]
}
get_my_obj = getById(73, myArray);

While there are many correct answers here, many of them do not address the fact that this is an unnecessarily expensive operation if done more than once. In an extreme case this could be the cause of real performance problems.
In the real world, if you are processing a lot of items and performance is a concern it's much faster to initially build a lookup:
var items = [{'id':'73','foo':'bar'},{'id':'45','foo':'bar'}];
var lookup = items.reduce((o,i)=>o[i.id]=o,{});
you can then get at items in fixed time like this :
var bar = o[id];
You might also consider using a Map instead of an object as the lookup: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Map

Recently, I have to face the same thing in which I need to search the string from a huge array.
After some search I found It'll be easy to handle with simple code:
Code:
var items = mydata.filter(function(item){
return item.word.toLowerCase().startsWith( 'gk );
})
See https://jsfiddle.net/maheshwaghmare/cfx3p40v/4/

Iterate over any item in the array. For every item you visit, check that item's id. If it's a match, return it.
If you just want teh codez:
function getId(array, id) {
for (var i = 0, len = array.length; i < len; i++) {
if (array[i].id === id) {
return array[i];
}
}
return null; // Nothing found
}
And the same thing using ECMAScript 5's Array methods:
function getId(array, id) {
var obj = array.filter(function (val) {
return val.id === id;
});
// Filter returns an array, and we just want the matching item.
return obj[0];
}

You may try out Sugarjs from http://sugarjs.com/.
It has a very sweet method on Arrays, .find. So you can find an element like this:
array.find( {id: 75} );
You may also pass an object with more properties to it to add another "where-clause".
Note that Sugarjs extends native objects, and some people consider this very evil...

As long as the browser supports ECMA-262, 5th edition (December 2009), this should work, almost one-liner:
var bFound = myArray.some(function (obj) {
return obj.id === 45;
});

Here's how I'd go about it in pure JavaScript, in the most minimal manner I can think of that works in ECMAScript 3 or later. It returns as soon as a match is found.
var getKeyValueById = function(array, key, id) {
var testArray = array.slice(), test;
while(test = testArray.pop()) {
if (test.id === id) {
return test[key];
}
}
// return undefined if no matching id is found in array
return;
}
var myArray = [{'id':'73', 'foo':'bar'}, {'id':'45', 'foo':'bar'}]
var result = getKeyValueById(myArray, 'foo', '45');
// result is 'bar', obtained from object with id of '45'

More generic and short
function findFromArray(array,key,value) {
return array.filter(function (element) {
return element[key] == value;
}).shift();
}
in your case Ex. var element = findFromArray(myArray,'id',45) that will give you the whole element.

We can use Jquery methods $.each()/$.grep()
var data= [];
$.each(array,function(i){if(n !== 5 && i > 4){data.push(item)}}
or
var data = $.grep(array, function( n, i ) {
return ( n !== 5 && i > 4 );
});
use ES6 syntax:
Array.find, Array.filter, Array.forEach, Array.map
Or use Lodash https://lodash.com/docs/4.17.10#filter, Underscore https://underscorejs.org/#filter

Building on the accepted answer:
jQuery:
var foo = $.grep(myArray, function(e){ return e.id === foo_id})
myArray.pop(foo)
Or CoffeeScript:
foo = $.grep myArray, (e) -> e.id == foo_id
myArray.pop foo

Use Array.prototype.filter() function.
DEMO: https://jsfiddle.net/sumitridhal/r0cz0w5o/4/
JSON
var jsonObj =[
{
"name": "Me",
"info": {
"age": "15",
"favColor": "Green",
"pets": true
}
},
{
"name": "Alex",
"info": {
"age": "16",
"favColor": "orange",
"pets": false
}
},
{
"name": "Kyle",
"info": {
"age": "15",
"favColor": "Blue",
"pets": false
}
}
];
FILTER
var getPerson = function(name){
return jsonObj.filter(function(obj) {
return obj.name === name;
});
}

You can do this even in pure JavaScript by using the in built "filter" function for arrays:
Array.prototype.filterObjects = function(key, value) {
return this.filter(function(x) { return x[key] === value; })
}
So now simply pass "id" in place of key and "45" in place of value, and you will get the full object matching an id of 45. So that would be,
myArr.filterObjects("id", "45");

I really liked the answer provided by Aaron Digulla but needed to keep my array of objects so I could iterate through it later. So I modified it to
var indexer = {};
for (var i = 0; i < array.length; i++) {
indexer[array[i].id] = parseInt(i);
}
//Then you can access object properties in your array using
array[indexer[id]].property

Use:
var retObj ={};
$.each(ArrayOfObjects, function (index, obj) {
if (obj.id === '5') { // id.toString() if it is int
retObj = obj;
return false;
}
});
return retObj;
It should return an object by id.

This solution may helpful as well:
Array.prototype.grep = function (key, value) {
var that = this, ret = [];
this.forEach(function (elem, index) {
if (elem[key] === value) {
ret.push(that[index]);
}
});
return ret.length < 2 ? ret[0] : ret;
};
var bar = myArray.grep("id","45");
I made it just like $.grep and if one object is find out, function will return the object, rather than an array.

Dynamic cached find
In this solution, when we search for some object, we save it in cache. This is middle point between "always search solutions" and "create hash-map for each object in precalculations".
let cachedFind = (()=>{
let cache = new Map();
return (arr,id,el=null) =>
cache.get(id) || (el=arr.find(o=> o.id==id), cache.set(id,el), el);
})();
// ---------
// TEST
// ---------
let myArray = [...Array(100000)].map((x,i)=> ({'id':`${i}`, 'foo':`bar_${i}`}));
// example usage
console.log( cachedFind(myArray,'1234').foo );
// Benchmark
let bench = (id) => {
console.time ('time for '+id );
console.log ( cachedFind(myArray,id).foo ); // FIND
console.timeEnd('time for '+id );
}
console.log('----- no cached -----');
bench(50000);
bench(79980);
bench(99990);
console.log('----- cached -----');
bench(79980); // cached
bench(99990); // cached

How to check if values in one JavaScript object are present in another one?

I am trying to compare json_str1 and json_str2, here it should return true as all elements in json_str1 are present in json_str2.
For now I am doing this the long way like this
json_str1 = '{"0":"a","1":"b","2":"c"}';
json_str2 = '{"0":"c","1":"b","2":"a"}';
json_obj1 = $.parseJSON(json_str1);
json_obj2 = $.parseJSON(json_str2);
arr1 = $.map(json_obj1, function(el) { return el });
arr2 = $.map(json_obj2, function(el) { return el });
if($(arr1).not(arr2).length === 0 && $(arr2).not(arr1).length === 0)
alert("equal");
else
alert("not equal");
How could I make it short and simple, without converting the objects into an array ?
https://jsfiddle.net/kq9gtdr0/

Use the following code:
Object.keys(json_obj1) . every(k1 =>
Object.keys(json_obj2) . some(k2 =>
json_obj1[k1] === json_obj2[k2]
)
);
In English:
Every key k1 in json_obj1 satisfies the condition that some key k2 in json_obj2 satisifies the condition that the value of json_obj1 with key k1 is equal to the value of json_obj2 with key k2.
Or in more conversational English:
Every value in the first object matches some value in the second.

Using lodash
var _ = require('lodash');
function compareValues(jstr1, jstr2) {
return _.isEqual(_.valuesIn(JSON.parse(jstr1)).sort(), _.valuesIn(JSON.parse(jstr2)).sort());
}
json_str1 = '{"0":"a","1":"b","2":"c"}';
json_str2 = '{"0":"c","1":"b","2":"a"}';
console.log(compareValues(json_str1, json_str2));

There is short and easy accurate way to this.
You can use a third party but extremely popular utility library called Lodash. Chaining functions you can check for equality.
First parse both JSON into objects
Then use _.values() to extract the values of all keys of each into separate arrays
Find difference of two arrays. If its an empty array then both of them are equal.
You can chain all the steps into one statement like:
_.isEmpty(_.difference(_.values(json_obj1), _.values(json_obj2)))
Example: https://jsfiddle.net/kq9gtdr0/4/
For more information:
https://lodash.com/docs#values
https://lodash.com/docs#difference
https://lodash.com/docs#isEmpty
You can include the library from CDN(https://cdn.jsdelivr.net/lodash/4.5.1/lodash.min.js) or download and use it as normal script. Lodash offers plenty of useful utility functions that makes JS programming a lot easier. You better try it out.

If you prefer using libraries, then you could use underscore isMatch
_.isMatch(object, properties)
Tells you if the keys and values in properties are contained in
object.

Extending the awesome answer by #user663031, in case you need to do deep comparison, here's code that works:
export function objectOneInsideObjectTwo(jsonObj1: any, jsonObj2: any): boolean {
return Object.keys(jsonObj1).every((k1) => {
if (parseType(jsonObj1[k1]) === 'dict') {
return objectOneInsideObjectTwo(jsonObj1[k1], jsonObj2[k1]);
}
if (parseType(jsonObj1[k1]) === 'array') {
const results: boolean[] = [];
jsonObj1[k1].forEach((o: any, i: number) => {
if (parseType(o) === 'dict') {
results.push(objectOneInsideObjectTwo(o, jsonObj2[k1][i]));
} else {
results.push(o === jsonObj2[k1][i]);
}
});
return results.every((r) => r);
}
return Object.keys(jsonObj2).some((k2) => jsonObj1[k1] === jsonObj2[k2]);
});
}
export function parseType<T>(v: T): string {
if (v === null || v === undefined) {
return 'null';
}
if (typeof v === 'object') {
if (v instanceof Array) {
return 'array';
}
if (v instanceof Date) {
return 'date';
}
return 'dict';
}
return typeof v;
}

You can try this
var json_str1 = {"0":"a","1":"b","2":"c"};
var json_str2 = {"0":"c","1":"b","2":"a"};
var flag = 1;
if(Object.keys(json_str1).length == Object.keys(json_str2).length){
Object.keys(json_str1).forEach(function(x){
if(!json_str2.hasOwnProperty(x) || json_str2[x] != json_str1[x]){
flag = 0;
return;
}
});
}
if(flag)
alert('equal');
else
alert('Not Equal');

If you want to find out if both Objects have the same keys there is no way to do this without at least converting the keys of both Objects to an array with Object.keys or looping through both Objects!
The reason is simple: It's clear that you have to compare the number of keys of both Objects and the only way to do this is by looping through all properties or Object.keys.
So I think the shortest way to do this is:
json_obj1 = JSON.parse('{"0":"a","1":"b","2":"c"}');
json_obj2 = JSON.parse('{"0":"c","1":"b","2":"a"}');
keys_1 = Object.keys(json_obj1);
keys_2 = Object.keys(json_obj2);
if(keys_1.length === keys_2.length && keys_1.every(key => keys_2.indexOf(key) >= 0)) {
alert('equal')
} else {
alert('not equal')
}
If you only want to check if all keys from json1 are present in json2 you can do:
json_obj1 = JSON.parse('{"0":"a","1":"b","2":"c"}');
json_obj2 = JSON.parse('{"0":"c","1":"b","2":"a"}');
if(Object.keys(json_obj1).every(key => key in json_obj2)) {
alert('equal');
} else {
alert('not equal');
}

In your question and comments you indicate you are only looking to verify that "all elements in json_str1 are present in json_str2". Your example code doesn't just do that, it checks for the complete equality of keys by testing if all the keys (not values) in the first object are in the second object AND all the keys in the second object are in the first object. By looking at your code, i assume that when you say "elements" you mean keys.
All that aside, this might help:
// Your first few lines of code
json_str1 = '{"0":"a","1":"b","2":"c"}';
json_str2 = '{"0":"c","1":"b","2":"a"}';
json_obj1 = $.parseJSON(json_str1);
json_obj2 = $.parseJSON(json_str2);
// My new code
var values1 = Object.keys(json_obj1).map(key => json_obj1[key]);
var values2 = Object.keys(json_obj2).map(key => json_obj2[key]);
// Check if every key in the first object is in the second object.
values1.every(k1 => values2.indexOf(k1) >= 0);
// OR
// Check for equality of keys by checking both directions.
values1.every(k1 => values2.indexOf(k1) >= 0) && values2.every(k2 => values1.indexOf(k2) >= 0);
That's 2 lines to get the keys, and one line to check. You only need one of those two checks.

How to test if two objects are the same with JavaScript?

I need a function:
function isSame(a, b){
}
In which, if a and b are the same, it returns true.
, I tried return a === b, but I found that [] === [] will return false.
Some results that I expect this function can gave:
isSame(3.14, 3.14); // true
isSame("hello", "hello"); // true
isSame([], []); // true
isSame([1, 2], [1, 2]); // true
isSame({ a : 1, b : 2}, {a : 1, b : 2}); //true
isSame([1, {a:1}], [1, {a:1}]); //true

You could embed Underscore.js and use _.isEqual(obj1, obj2).
The function works for arbitrary objects and uses whatever is the most efficient way to test the given objects for equality.

the best way to do that is to use a JSON serializer. serialize both to string and compare the string.

There are some examples, adapted from scheme, on Crockford's site. Specifically, check out:
function isEqual(s1, s2) {
return isAtom(s1) && isAtom(s2) ? isEqan(s1, s2) :
isAtom(s1) || isAtom(s2) ? false :
isEqlist(s1, s2);
}
It can all be found here:
http://javascript.crockford.com/little.js
Here is a working example:
http://jsfiddle.net/FhGpd/
Update:
Just wrote some test cases based on the OP. Turns out I needed to modify the sub1 function to check <= 0 not === 0 otherwise isEqual(3.14, 3.14) blew the stack. Also, isEqual does not work for object comparison, so you are on your own there. However, if you follow the examples on Crockford's site you will see how easy and fun it is to write recursive methods that could be used to check for object equality.

Here is something that can work:
function isSame(obj1, obj2, prefer){
// Optional parameter prefer allows to only check for object keys and not both keys and values of an object
var obj_prefer = prefer || "both";
function checkArray(arr1, arr2){
for(var i = 0, j = obj1.length; i<j; i++){
if(obj1[i] !== obj2[i]){return false;}
}
return true;
}
function checkValues(obj_1, obj_2){
for(var prop in obj_1){
if(typeof obj_1[prop] === "function"){ // converting functions to string so that they can be matched
obj_1[prop] = String(obj_1[prop]);
obj_2[prop] = String(obj_2[prop]);
}
if(obj_1[prop] !== obj_2[prop]){ return false;}
}
return true;
}
// The built in === will check everything except when typeof object is "object"
if ( typeof obj1 === "object"){
// typeof Array is object so this is an alternative
if((typeof obj1.push === "function") && (!obj1.hasOwnProperty('push'))){
return checkArray(obj1, obj2);
}
else{
if( obj_prefer !== "keys"){ // do not check for values if obj_prefer is "keys"
return checkValues(obj1, obj2);
}
var keys_1 = Object.keys(obj1);
var keys_2 = Object.keys(obj2);
if(!checkArray(keys_1, keys_2)){return false;}
return true;
}
}
// I thought undefined === undefined will give false but it isn't so you can remove it
if( typeof obj1 === "undefined" && typeof obj2 === "undefined" ){return true}
if(typeof obj1 === "function"){
return String(obj1) === String(obj2);
}
return obj1 === obj2;
}
console.log(isSame(2, 2)); //true
console.log(isSame([1], [1])); // true
Since it converts Functions into Strings to compare them, check out for spaces as that can break things:
var func1 = function(){},
func2 = function(){ }; // function with extra space
isSame(func1, func2); // false
You can check out http://jsfiddle.net/webholik/dwaLN/4/ to try it yourself.

If anyone reading this answer is using Angular.js, you can use angular.equals(obj1,obj2);
According to the docs:
Determines if two objects or two values are equivalent. Supports value
types, regular expressions, arrays and objects.
Two objects or values are considered equivalent if at least one of the
following is true:
Both objects or values pass === comparison.
Both objects or values are of the same type and all of their properties are equal by comparing them with angular.equals.
Both values are NaN. (In JavaScript, NaN == NaN => false. But we consider two NaN as equal).
Both values represent the same regular expression (In JavaScript, /abc/ == /abc/ => false. But we consider two regular expressions as
equal when their textual representation matches).
During a property comparison, properties of function type and properties with names that begin with $ are ignored.
Scope and DOMWindow objects are being compared only by identify (===).

How to determine if object is in array [duplicate]

This question already has answers here:
How do I check if an array includes a value in JavaScript?
(60 answers)
Closed 29 days ago.
I need to determine if an object already exists in an array in javascript.
eg (dummycode):
var carBrands = [];
var car1 = {name:'ford'};
var car2 = {name:'lexus'};
var car3 = {name:'maserati'};
var car4 = {name:'ford'};
carBrands.push(car1);
carBrands.push(car2);
carBrands.push(car3);
carBrands.push(car4);
now the "carBrands" array contains all instances.
I'm now looking a fast solution to check if an instance of car1, car2, car3 or car4 is already in the carBrands array.
eg:
var contains = carBrands.Contains(car1); //<--- returns bool.
car1 and car4 contain the same data but are different instances they should be tested as not equal.
Do I have add something like a hash to the objects on creation? Or is there a faster way to do this in Javascript.
I am looking for the fastest solution here, if dirty, so it has to be ;) In my app it has to deal with around 10000 instances.
no jquery

Use something like this:
function containsObject(obj, list) {
var i;
for (i = 0; i < list.length; i++) {
if (list[i] === obj) {
return true;
}
}
return false;
}
In this case, containsObject(car4, carBrands) is true. Remove the carBrands.push(car4); call and it will return false instead. If you later expand to using objects to store these other car objects instead of using arrays, you could use something like this instead:
function containsObject(obj, list) {
var x;
for (x in list) {
if (list.hasOwnProperty(x) && list[x] === obj) {
return true;
}
}
return false;
}
This approach will work for arrays too, but when used on arrays it will be a tad slower than the first option.

Why don't you use the indexOf method of javascript arrays?
Check this out: MDN indexOf Arrays
Simply do:
carBrands.indexOf(car1);
It will return you the index (position in the array) of car1. It will return -1 if car1 was not found in the array.
http://jsfiddle.net/Fraximus/r154cd9o
Edit: Note that in the question, the requirements are to check for the same object referenced in the array, and NOT a new object. Even if the new object is identical in content to the object in the array, it is still a different object.
As mentioned in the comments, objects are passed by reference in JS and the same object can exist multiple times in multiple structures.
If you want to create a new object and check if the array contains objects identical to your new one, this answer won't work (Julien's fiddle below), if you want to check for that same object's existence in the array, then this answer will work. Check out the fiddles here and in the comments.

Having been recently bitten by the FP bug reading many wonderful accounts of how neatly the functional paradigm fits with Javascript
I replicate the code for completeness sake and suggest two ways this can be done functionally.
var carBrands = [];
var car1 = {name:'ford'};
var car2 = {name:'lexus'};
var car3 = {name:'maserati'};
var car4 = {name:'ford'};
var car5 = {name:'toyota'};
carBrands.push(car1);
carBrands.push(car2);
carBrands.push(car3);
carBrands.push(car4);
// ES6 approach which uses the includes method (Chrome47+, Firefox43+)
carBrands.includes(car1) // -> true
carBrands.includes(car5) // -> false
If you need to support older browsers use the polyfill, it seems IE9+ and Edge do NOT support it. Located in polyfill section of MSDN page
Alternatively I would like to propose an updated answer to cdhowie
// ES2015 syntax
function containsObject(obj, list) {
return list.some(function(elem) {
return elem === obj
})
}
// or ES6+ syntax with cool fat arrows
function containsObject(obj, list) {
return list.some(elem => elem === obj)
}

try Array.prototype.some()
MDN Array.prototype.some
function isBiggerThan10(element, index, array) {
return element > 10;
}
[2, 5, 8, 1, 4].some(isBiggerThan10); // false
[12, 5, 8, 1, 4].some(isBiggerThan10); // true

You could use jQuery's grep method:
$.grep(carBrands, function(obj) { return obj.name == "ford"; });
But as you specify no jQuery, you could just make a derivative of the function. From the source code:
function grepArray( elems, callback, inv ) {
var ret = [];
// Go through the array, only saving the items
// that pass the validator function
for ( var i = 0, length = elems.length; i < length; i++ ) {
if ( !inv !== !callback( elems[ i ], i ) ) {
ret.push( elems[ i ] );
}
}
return ret;
}
grepArray(carBrands, function(obj) { return obj.name == "ford"; });

I used underscore javascript library to tweak this issue.
function containsObject(obj, list) {
var res = _.find(list, function(val){ return _.isEqual(obj, val)});
return (_.isObject(res))? true:false;
}
please refer to underscore.js documentation for the underscore functions used in the above example.
note: This is not a pure javascript solution. Shared for educational purposes.

You can just use the equality operator: ==. Objects are checked by reference by default, so you don't even need to use the === operator.
try this, just make sure you're using the correct variable reference in the place of car1:
var i, car, l = cars.length;
for (i = 0; i < l; i++)
{
if ((car = cars[i]) == car1)
{
break;
}
else car = null;
}
Edit to add:
An array extension was mentioned, so here's the code for it:
Array.prototype.contains = Array.prototype.contains || function(obj)
{
var i, l = this.length;
for (i = 0; i < l; i++)
{
if (this[i] == obj) return true;
}
return false;
};
Note that I'm caching the length value, as the Array's length property is actually an accessor, which is marginally slower than an internal variable.

I would use a generic iterator of property/value over the array. No jQuery required.
arr = [{prop1: 'val1', prop2: 'val2'}, {prop1: 'val3', prop2: 'val4'}];
objectPropInArray(arr, 'prop1', 'val3'); // <-- returns true
function objectPropInArray(list, prop, val) {
if (list.length > 0 ) {
for (i in list) {
if (list[i][prop] === val) {
return true;
}
}
}
return false;
}

You could try sorting the array based on a property, like so:
carBrands = carBrands.sort(function(x,y){
return (x == y) ? 0 : (x > y) ? 1 : -1;
});
Then you can use an iterative routine to check whether
carBrands[Math.floor(carBrands.length/2)]
// change carBrands.length to a var that keeps
// getting divided by 2 until result is the target
// or no valid target exists
is greater or lesser than the target, and so on, which will let you go through the array quickly to find whether the object exists or not.

try this ,
You can use the JavaScript some() method to find out if a JavaScript array contains an object.
<script>
// An array of objects
var persons = [{name: "Harry"}, {name: "Alice"}, {name: "Peter"}];
// Find if the array contains an object by comparing the property value
if(persons.some(person => person.name === "Peter")){
alert("Object found inside the array.");
} else{
alert("Object not found.");
}
</script>

EDIT 05/18/2022
The most simple way using ES6:
const arrayContainsObject = <T extends Record<string, unknown>>(array: T[], object: T) => {
return array.some(item => Object.keys(item).every(key => item[key] === object[key]))
}
Use like so:
const arr = [{
prop1: 'value1',
prop2: 'value2'
}]
const obj1 = {
prop1: 'value1',
prop2: 'value2'
}
const obj2 = {
prop2: 'value2',
prop1: 'value1'
}
const obj3 = {
prop0: 'value0',
prop1: 'value1'
}
arrayContainsObject(arr, obj1) // true
arrayContainsObject(arr, obj2) // true, even when props are arranged in different order
arrayContainsObject(arr, obj3) // false
Previous answer, don't use (because the order of props in an object needs to be identical)
const arr = [{
prop: 'value'
}]
const obj = {
prop: 'value'
}
arr.some((e) => Object.entries(e).toString() === Object.entries(obj).toString()) // true

i know this is an old post, but i wanted to provide a JQuery plugin version and my code.
// Find the first occurrence of object in list, Similar to $.grep, but stops searching
function findFirst(a,b){
var i; for (i = 0; i < a.length; ++i) { if (b(a[i], i)) return a[i]; } return undefined;
}
usage:
var product = $.findFirst(arrProducts, function(p) { return p.id == 10 });

This function is to check for a unique field.
Arg 1: the array with selected data
Arg 2: key to check
Arg 3: value that must be "validated"
function objectUnique( array, field, value )
{
var unique = true;
array.forEach(function ( entry )
{
if ( entry[field] == value )
{
unique = false;
}
});
return unique;
}

you can use Array.find().
in your case is going to look like this
carBrands.find(function(car){
let result = car.name === 'ford'
if (result == null){
return false;
} else {
return true
}
});
if car is not null it will return the javaScript Object which contains the string 'ford'

The issue with many of the answers here is that they will NOT find an object in an array that is equal to another object. They will only search for an EXISTING object that has a pointer to it in an array.
Quick fix using lodash to see if ANY equal object is in an array:
import _ from 'lodash';
_.find(carBrands, car1); //returns object if true, undefined if false
Working Plunker using this method: https://plnkr.co/edit/y2YX9o7zkQa2r7lJ

if its possible to use es6
carBrands.filter(carBrand => carBrand.name === carX.name).length > 0
if it's true there is a similarity

You can convert both the JSON objects to string and simply check if the bigger json contains the smaller json.
console.log(JSON.stringify(carBrands).includes(JSON.stringify(car1))); // true
console.log(JSON.stringify(carBrands).includes(JSON.stringify(car5))); // false

You could also a the findIndex
var carBrands = [];
var car1 = {name:'ford'};
var car2 = {name:'lexus'};
carBrands.push(car1);
if (carBrands.findIndex(f => f.name === car1.name) === -1) {
console.log('not contain')
} else {
console.log('contain')
}
if (carBrands.findIndex(f => f.name === car2.name) === -1) {
console.log('not contain')
} else {
console.log('contain')
}

Detect if parameter passed is an array? Javascript [duplicate]

This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
How to detect if a variable is an array
I have a simple question:
How do I detect if a parameter passed to my javascript function is an array? I don't believe that I can test:
if (typeof paramThatCouldBeArray == 'array')
So is it possible?
How would I do it?
Thanks in advance.

if (param instanceof Array)
...
Edit. As of 2016, there is a ready-built method that catches more corner cases, Array.isArray, used as follows:
if (Array.isArray(param))
...

This is the approach jQuery 1.4.2 uses:
var toString = param.prototype.toString;
var isArray = function(obj) {
return toString.call(obj) === "[object Array]";
}

I found this here:
function isArray(obj) {
return obj.constructor == Array;
}
also this one
function isArray(obj) {
return (obj.constructor.toString().indexOf(”Array”) != -1);
}

You can test the constructor property:
if (param.constructor == Array) {
...
}
Though this will include objects that have an array prototype,
function Stack() {
}
Stack.prototype = [];
unless they also define constructor:
Stack.prototype.constructor = Stack;
or:
function Stack() {
this.constructor = Stack;
}

Some days ago I was building a simple type detection function, maybe its useful for you:
Usage:
//...
if (typeString(obj) == 'array') {
//..
}
Implementation:
function typeString(o) {
if (typeof o != 'object')
return typeof o;
if (o === null)
return "null";
//object, array, function, date, regexp, string, number, boolean, error
var internalClass = Object.prototype.toString.call(o)
.match(/\[object\s(\w+)\]/)[1];
return internalClass.toLowerCase();
}
The second variant of this function is more strict, because it returns only object types described in the ECMAScript specification (possible output values: "object", "undefined", "null", and "function", "array", "date", "regexp", "string", "number", "boolean" "error", using the [[Class]] internal property).

Duck Typying
Actually, you don't necessarily want to check that an object is an array. You should duck type it and the only thing you want that object to implement is the length property. After this you can transform it into an array:
var arrayLike = {
length : 3,
0: "foo"
};
// transform object to array
var array = Array.prototype.slice.call(arrayLike);
JSON.stringify(array); // ["foo", null, null]
Array.prototype.slice.call(object) will transform into an array every object that exposes a length property. In the case of strings for example:
var array = Array.prototype.slice.call("123");
JSON.stringify(array); // ["1", "2", "3"]
Well, this technique it's not quite working on IE6 (I don't know about later versions), but it's easy to create a small utility function to transform objects in arrays.