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After an AJAX request, sometimes my application may return an empty object, like:
var a = {};
How can I check whether that's the case?
ECMA 5+:
// because Object.keys(new Date()).length === 0;
// we have to do some additional check
obj // 👈 null and undefined check
&& Object.keys(obj).length === 0
&& Object.getPrototypeOf(obj) === Object.prototype
Note, though, that this creates an unnecessary array (the return value of keys).
Pre-ECMA 5:
function isEmpty(obj) {
for(var prop in obj) {
if(Object.prototype.hasOwnProperty.call(obj, prop)) {
return false;
}
}
return JSON.stringify(obj) === JSON.stringify({});
}
jQuery:
jQuery.isEmptyObject({}); // true
lodash:
_.isEmpty({}); // true
Underscore:
_.isEmpty({}); // true
Hoek
Hoek.deepEqual({}, {}); // true
ExtJS
Ext.Object.isEmpty({}); // true
AngularJS (version 1)
angular.equals({}, {}); // true
Ramda
R.isEmpty({}); // true
If ECMAScript 5 support is available, you can use Object.keys():
function isEmpty(obj) {
return Object.keys(obj).length === 0;
}
For ES3 and older, there's no easy way to do this. You'll have to loop over the properties explicitly:
function isEmpty(obj) {
for(var prop in obj) {
if(obj.hasOwnProperty(prop))
return false;
}
return true;
}
For those of you who have the same problem but use jQuery, you can use jQuery.isEmptyObject.
Performance
Today 2020.01.17, I performed tests on macOS High Sierra 10.13.6 on Chrome v79.0, Safari v13.0.4, and Firefox v72.0; for the chosen solutions.
Conclusions
Solutions based on for-in (A, J, L, M) are fastest
Solutions based on JSON.stringify (B, K) are slow
Surprisingly, the solution based on Object (N) is also slow
NOTE: This table does not match the photo below.
Details
There are 15 solutions presented in the snippet below.
If you want to run a performance test on your machine, click HERE.
This link was updated 2021.07.08, but tests originally were performed here - and results in the table above came from there (but now it looks like that service no longer works).
var log = (s, f) => console.log(`${s} --> {}:${f({})} {k:2}:${f({ k: 2 })}`);
function A(obj) {
for (var i in obj) return false;
return true;
}
function B(obj) {
return JSON.stringify(obj) === "{}";
}
function C(obj) {
return Object.keys(obj).length === 0;
}
function D(obj) {
return Object.entries(obj).length === 0;
}
function E(obj) {
return Object.getOwnPropertyNames(obj).length === 0;
}
function F(obj) {
return Object.keys(obj).length === 0 && obj.constructor === Object;
}
function G(obj) {
return typeof obj === "undefined" || !Boolean(Object.keys(obj)[0]);
}
function H(obj) {
return Object.entries(obj).length === 0 && obj.constructor === Object;
}
function I(obj) {
return Object.values(obj).every((val) => typeof val === "undefined");
}
function J(obj) {
for (const key in obj) {
if (hasOwnProperty.call(obj, key)) {
return false;
}
}
return true;
}
function K(obj) {
for (var prop in obj) {
if (obj.hasOwnProperty(prop)) {
return false;
}
}
return JSON.stringify(obj) === JSON.stringify({});
}
function L(obj) {
for (var prop in obj) {
if (obj.hasOwnProperty(prop)) return false;
}
return true;
}
function M(obj) {
for (var k in obj) {
if (obj.hasOwnProperty(k)) {
return false;
}
}
return true;
}
function N(obj) {
return (
Object.getOwnPropertyNames(obj).length === 0 &&
Object.getOwnPropertySymbols(obj).length === 0 &&
Object.getPrototypeOf(obj) === Object.prototype
);
}
function O(obj) {
return !(Object.getOwnPropertyNames !== undefined
? Object.getOwnPropertyNames(obj).length !== 0
: (function () {
for (var key in obj) break;
return key !== null && key !== undefined;
})());
}
log("A", A);
log("B", B);
log("C", C);
log("D", D);
log("E", E);
log("F", F);
log("G", G);
log("H", H);
log("I", I);
log("J", J);
log("K", K);
log("L", L);
log("M", M);
log("N", N);
log("O", O);
You can use Underscore.js.
_.isEmpty({}); // true
if(Object.getOwnPropertyNames(obj).length === 0){
//is empty
}
see http://bencollier.net/2011/04/javascript-is-an-object-empty/
How about using JSON.stringify? It is almost available in all modern browsers.
function isEmptyObject(obj){
return JSON.stringify(obj) === '{}';
}
There is a simple way if you are on a newer browser.
Object.keys(obj).length === 0
Old question, but just had the issue. Including JQuery is not really a good idea if your only purpose is to check if the object is not empty. Instead, just deep into JQuery's code, and you will get the answer:
function isEmptyObject(obj) {
var name;
for (name in obj) {
if (obj.hasOwnProperty(name)) {
return false;
}
}
return true;
}
Using Object.keys(obj).length (as suggested above for ECMA 5+) is 10 times slower for empty objects! keep with the old school (for...in) option.
Tested under Node, Chrome, Firefox and IE 9, it becomes evident that for most use cases:
(for...in...) is the fastest option to use!
Object.keys(obj).length is 10 times slower for empty objects
JSON.stringify(obj).length is always the slowest (not suprising)
Object.getOwnPropertyNames(obj).length takes longer than Object.keys(obj).length can be much longer on some systems.
Bottom line performance wise, use:
function isEmpty(obj) {
for (var x in obj) { return false; }
return true;
}
or
function isEmpty(obj) {
for (var x in obj) { if (obj.hasOwnProperty(x)) return false; }
return true;
}
See detailed testing results and test code at Is object empty?
My take:
function isEmpty(obj) {
return Object.keys(obj).length === 0;
}
var a = {
a: 1,
b: 2
}
var b = {}
console.log(isEmpty(a)); // false
console.log(isEmpty(b)); // true
Just, I don't think all browsers implement Object.keys() currently.
I am using this.
function isObjectEmpty(object) {
var isEmpty = true;
for (keys in object) {
isEmpty = false;
break; // exiting since we found that the object is not empty
}
return isEmpty;
}
Eg:
var myObject = {}; // Object is empty
var isEmpty = isObjectEmpty(myObject); // will return true;
// populating the object
myObject = {"name":"John Smith","Address":"Kochi, Kerala"};
// check if the object is empty
isEmpty = isObjectEmpty(myObject); // will return false;
from here
Update
OR
you can use the jQuery implementation of isEmptyObject
function isEmptyObject(obj) {
var name;
for (name in obj) {
return false;
}
return true;
}
Just a workaround. Can your server generate some special property in case of no data?
For example:
var a = {empty:true};
Then you can easily check it in your AJAX callback code.
Another way to check it:
if (a.toSource() === "({})") // then 'a' is empty
EDIT:
If you use any JSON library (f.e. JSON.js) then you may try JSON.encode() function and test the result against empty value string.
1. Using Object.keys
Object.keys will return an Array, which contains the property names of the object. If the length of the array is 0, then we know that the object is empty.
function isEmpty(obj) {
return Object.keys(obj).length === 0 && obj.constructor === Object;
}
We can also check this using Object.values and Object.entries.
This is typically the easiest way to determine if an object is empty.
2. Looping over object properties with for…in
The for…in statement will loop through the enumerable property of object.
function isEmpty(obj) {
for(var prop in obj) {
if(obj.hasOwnProperty(prop))
return false;
}
return true;
}
In the above code, we will loop through object properties and if an object has at least one property, then it will enter the loop and return false. If the object doesn’t have any properties then it will return true.
#3. Using JSON.stringify
If we stringify the object and the result is simply an opening and closing bracket, we know the object is empty.
function isEmptyObject(obj){
return JSON.stringify(obj) === '{}';
}
4. Using jQuery
jQuery.isEmptyObject(obj);
5. Using Underscore and Lodash
_.isEmpty(obj);
Resource
function isEmpty(obj) {
for(var i in obj) { return false; }
return true;
}
The following example show how to test if a JavaScript object is empty, if by empty we means has no own properties to it.
The script works on ES6.
const isEmpty = (obj) => {
if (obj === null ||
obj === undefined ||
Array.isArray(obj) ||
typeof obj !== 'object'
) {
return true;
}
return Object.getOwnPropertyNames(obj).length === 0;
};
console.clear();
console.log('-----');
console.log(isEmpty('')); // true
console.log(isEmpty(33)); // true
console.log(isEmpty([])); // true
console.log(isEmpty({})); // true
console.log(isEmpty({ length: 0, custom_property: [] })); // false
console.log('-----');
console.log(isEmpty('Hello')); // true
console.log(isEmpty([1, 2, 3])); // true
console.log(isEmpty({ test: 1 })); // false
console.log(isEmpty({ length: 3, custom_property: [1, 2, 3] })); // false
console.log('-----');
console.log(isEmpty(new Date())); // true
console.log(isEmpty(Infinity)); // true
console.log(isEmpty(null)); // true
console.log(isEmpty(undefined)); // true
The correct answer is:
function isEmptyObject(obj) {
return (
Object.getPrototypeOf(obj) === Object.prototype &&
Object.getOwnPropertyNames(obj).length === 0 &&
Object.getOwnPropertySymbols(obj).length === 0
);
}
This checks that:
The object's prototype is exactly Object.prototype.
The object has no own properties (regardless of enumerability).
The object has no own property symbols.
In other words, the object is indistinguishable from one created with {}.
jQuery have special function isEmptyObject() for this case:
jQuery.isEmptyObject({}) // true
jQuery.isEmptyObject({ foo: "bar" }) // false
Read more on http://api.jquery.com/jQuery.isEmptyObject/
Caveat! Beware of JSON's limitiations.
javascript:
obj={ f:function(){} };
alert( "Beware!! obj is NOT empty!\n\nobj = { f:function(){} }" +
"\n\nJSON.stringify( obj )\n\nreturns\n\n" +
JSON.stringify( obj ) );
displays
Beware!! obj is NOT empty!
obj = { f:function(){} }
JSON.stringify( obj )
returns
{}
To really accept ONLY {}, the best way to do it in Javascript using Lodash is:
_.isEmpty(value) && _.isPlainObject(value)
In addition to Thevs answer:
var o = {};
alert($.toJSON(o)=='{}'); // true
var o = {a:1};
alert($.toJSON(o)=='{}'); // false
it's jquery + jquery.json
Sugar.JS provides extended objects for this purpose. The code is clean and simple:
Make an extended object:
a = Object.extended({})
Check it's size:
a.size()
Pure Vanilla Javascript, and full backward compatibility
function isObjectDefined (Obj) {
if (Obj === null || typeof Obj !== 'object' ||
Object.prototype.toString.call(Obj) === '[object Array]') {
return false
} else {
for (var prop in Obj) {
if (Obj.hasOwnProperty(prop)) {
return true
}
}
return JSON.stringify(Obj) !== JSON.stringify({})
}
}
console.log(isObjectDefined()) // false
console.log(isObjectDefined('')) // false
console.log(isObjectDefined(1)) // false
console.log(isObjectDefined('string')) // false
console.log(isObjectDefined(NaN)) // false
console.log(isObjectDefined(null)) // false
console.log(isObjectDefined({})) // false
console.log(isObjectDefined([])) // false
console.log(isObjectDefined({a: ''})) // true
IsEmpty Object, unexpectedly lost its meaning i.e.: it's programming semantics, when our famous guru from Yahoo introduced the customized non-enumerable Object properties to ECMA and they got accepted.
[ If you don't like history - feel free to skip right to the working code ]
I'm seeing lots of good answers \ solutions to this question \ problem.
However, grabbing the most recent extensions to ECMA Script is not the honest way to go. We used to hold back the Web back in the day to keep Netscape 4.x, and Netscape based pages work and projects alive, which (by the way) were extremely primitive backwards and idiosyncratic, refusing to use new W3C standards and propositions [ which were quite revolutionary for that time and coder friendly ] while now being brutal against our own legacy.
Killing Internet Explorer 11 is plain wrong! Yes, some old warriors that infiltrated Microsoft remaining dormant since the "Cold War" era, agreed to it - for all the wrong reasons. - But that doesn't make it right!
Making use, of a newly introduced method\property in your answers and handing it over as a discovery ("that was always there but we didn't notice it"), rather than a new invention (for what it really is), is somewhat 'green' and harmful. I used to make such mistakes some 20 years ago when I still couldn't tell what's already in there and treated everything I could find a reference for, as a common working solution...
Backward compatibility is important !
We just don't know it yet. That's the reason I got the need to share my 'centuries old' generic solution which remains backward and forward compatible to the unforeseen future.
There were lots of attacks on the in operator but I think the guys doing that have finally come to senses and really started to understand and appreciate a true Dynamic Type Language such as JavaScript and its beautiful nature.
My methods aim to be simple and nuclear and for reasons mentioned above, I don't call it "empty" because the meaning of that word is no longer accurate. Is Enumerable, seems to be the word with the exact meaning.
function isEnum( x ) { for( var p in x )return!0; return!1 };
Some use cases:
isEnum({1:0})
true
isEnum({})
false
isEnum(null)
false
Thanks for reading!
Best one-liner solution I could find (updated):
isEmpty = obj => !Object.values(obj).filter(e => typeof e !== 'undefined').length;
console.log(isEmpty({})) // true
console.log(isEmpty({a: undefined, b: undefined})) // true
console.log(isEmpty({a: undefined, b: void 1024, c: void 0})) // true
console.log(isEmpty({a: [undefined, undefined]})) // false
console.log(isEmpty({a: 1})) // false
console.log(isEmpty({a: ''})) // false
console.log(isEmpty({a: null, b: undefined})) // false
Another alternative is to use is.js (14kB) as opposed to jquery (32kB), lodash (50kB), or underscore (16.4kB). is.js proved to be the fastest library among aforementioned libraries that could be used to determine whether an object is empty.
http://jsperf.com/check-empty-object-using-libraries
Obviously all these libraries are not exactly the same so if you need to easily manipulate the DOM then jquery might still be a good choice or if you need more than just type checking then lodash or underscore might be good. As for is.js, here is the syntax:
var a = {};
is.empty(a); // true
is.empty({"hello": "world"}) // false
Like underscore's and lodash's _.isObject(), this is not exclusively for objects but also applies to arrays and strings.
Under the hood this library is using Object.getOwnPropertyNames which is similar to Object.keys but Object.getOwnPropertyNames is a more thorough since it will return enumerable and non-enumerable properties as described here.
is.empty = function(value) {
if(is.object(value)){
var num = Object.getOwnPropertyNames(value).length;
if(num === 0 || (num === 1 && is.array(value)) || (num === 2 && is.arguments(value))){
return true;
}
return false;
} else {
return value === '';
}
};
If you don't want to bring in a library (which is understandable) and you know that you are only checking objects (not arrays or strings) then the following function should suit your needs.
function isEmptyObject( obj ) {
return Object.getOwnPropertyNames(obj).length === 0;
}
This is only a bit faster than is.js though just because you aren't checking whether it is an object.
I know this doesn't answer 100% your question, but I have faced similar issues before and here's how I use to solve them:
I have an API that may return an empty object. Because I know what fields to expect from the API, I only check if any of the required fields are present or not.
For example:
API returns {} or {agentID: '1234' (required), address: '1234 lane' (opt),...}.
In my calling function, I'll only check
if(response.data && response.data.agentID) {
do something with my agentID
} else {
is empty response
}
This way I don't need to use those expensive methods to check if an object is empty. The object will be empty for my calling function if it doesn't have the agentID field.
We can check with vanilla js with handling null or undefined check also as follows,
function isEmptyObject(obj) {
return !!obj && Object.keys(obj).length === 0 && obj.constructor === Object;
}
//tests
isEmptyObject(new Boolean()); // false
isEmptyObject(new Array()); // false
isEmptyObject(new RegExp()); // false
isEmptyObject(new String()); // false
isEmptyObject(new Number()); // false
isEmptyObject(new Function()); // false
isEmptyObject(new Date()); // false
isEmptyObject(null); // false
isEmptyObject(undefined); // false
isEmptyObject({}); // true
I liked this one I came up with, with the help of some other answers here. Thought I'd share it.
Object.defineProperty(Object.prototype, 'isEmpty', {
get() {
for(var p in this) {
if (this.hasOwnProperty(p)) {return false}
}
return true;
}
});
let users = {};
let colors = {primary: 'red'};
let sizes = {sm: 100, md: 200, lg: 300};
console.log(
'\nusers =', users,
'\nusers.isEmpty ==> ' + users.isEmpty,
'\n\n-------------\n',
'\ncolors =', colors,
'\ncolors.isEmpty ==> ' + colors.isEmpty,
'\n\n-------------\n',
'\nsizes =', sizes,
'\nsizes.isEmpty ==> ' + sizes.isEmpty,
'\n',
''
);
It's weird that I haven't encountered a solution that compares the object's values as opposed to the existence of any entry (maybe I missed it among the many given solutions).
I would like to cover the case where an object is considered empty if all its values are undefined:
const isObjectEmpty = obj => Object.values(obj).every(val => typeof val === "undefined")
console.log(isObjectEmpty({})) // true
console.log(isObjectEmpty({ foo: undefined, bar: undefined })) // true
console.log(isObjectEmpty({ foo: false, bar: null })) // false
Example usage
Let's say, for the sake of example, you have a function (paintOnCanvas) that destructs values from its argument (x, y and size). If all of them are undefined, they are to be left out of the resulting set of options. If not they are not, all of them are included.
function paintOnCanvas ({ brush, x, y, size }) {
const baseOptions = { brush }
const areaOptions = { x, y, size }
const options = isObjectEmpty(areaOptions) ? baseOptions : { ...baseOptions, areaOptions }
// ...
}
Related
Often while using JavaScript you run into silly problems. One such problems is discerning between Object types.
Is there a way to create a function with this functionality? See Below:
_discern = function () { [ function code ] };
_discern({}); // Logs: Object
_discern([]); // Logs: Array
_discern(document); // Logs: Pseudo-Object
_discern(document.querySelectorAll("*")); // Logs: Pseudo-Array
I've already tried creating a function that checks for array-likeness, but that didn't work as good as I had hoped:
isArrLike = function (_) {
_[0] = 0; return [].slice.call(_).length >= Object.values(_).length;
};
And I've tried using that behavior into another function. All failures. Is there a way?
Looks like you want to know if something behaves like an array, instead of looking for the actual type/constructor.
If that's the case, it should be enough to check if something is iterable:
function isIterable(obj) {
// checks for null and undefined
if (obj == null) {
return false;
}
return typeof obj[Symbol.iterator] === 'function';
}
All of these are objects:
is array → return x instanceof Array or Array.isArray(x)
is function → return typeof x === 'function'
is HTML element → return x instanceof HTMLElement
is plain object → return typeof x === 'object' && /* ... is not array, not function, not HTML element */
Thanks to Logain's answer, I can solve the problem. Here's my approach:
kind = function (a) {
let u = toString.call(a.valueOf()).slice(8, -1);
if (a == null || u == "String" || u == "Number" || u == "Boolean") {
return u;
}
else if (typeof a[Symbol.iterator] == "function") {
return u != "Array" ? "Array-Like" : u;
}
else {
return u;
}
};
Let's say we have this JavaScript object:
var object = {
innerObject:{
deepObject:{
value:'Here am I'
}
}
};
How can we check if value property exists?
I can see only two ways:
First one:
if(object && object.innerObject && object.innerObject.deepObject && object.innerObject.deepObject.value) {
console.log('We found it!');
}
Second one:
if(object.hasOwnProperty('innerObject') && object.innerObject.hasOwnProperty('deepObject') && object.innerObject.deepObject.hasOwnProperty('value')) {
console.log('We found it too!');
}
But is there a way to do a deep check? Let's say, something like:
object['innerObject.deepObject.value']
or
object.hasOwnProperty('innerObject.deepObject.value')
There isn't a built-in way for this kind of check, but you can implement it easily. Create a function, pass a string representing the property path, split the path by ., and iterate over this path:
Object.prototype.hasOwnNestedProperty = function(propertyPath) {
if (!propertyPath)
return false;
var properties = propertyPath.split('.');
var obj = this;
for (var i = 0; i < properties.length; i++) {
var prop = properties[i];
if (!obj || !obj.hasOwnProperty(prop)) {
return false;
} else {
obj = obj[prop];
}
}
return true;
};
// Usage:
var obj = {
innerObject: {
deepObject: {
value: 'Here am I'
}
}
}
console.log(obj.hasOwnNestedProperty('innerObject.deepObject.value'));
You could make a recursive method to do this.
The method would iterate (recursively) on all 'object' properties of the object you pass in and return true as soon as it finds one that contains the property you pass in. If no object contains such property, it returns false.
var obj = {
innerObject: {
deepObject: {
value: 'Here am I'
}
}
};
function hasOwnDeepProperty(obj, prop) {
if (typeof obj === 'object' && obj !== null) { // only performs property checks on objects (taking care of the corner case for null as well)
if (obj.hasOwnProperty(prop)) { // if this object already contains the property, we are done
return true;
}
for (var p in obj) { // otherwise iterate on all the properties of this object.
if (obj.hasOwnProperty(p) && // and as soon as you find the property you are looking for, return true
hasOwnDeepProperty(obj[p], prop)) {
return true;
}
}
}
return false;
}
console.log(hasOwnDeepProperty(obj, 'value')); // true
console.log(hasOwnDeepProperty(obj, 'another')); // false
Alternative recursive function:
Loops over all object keys. For any key it checks if it is an object, and if so, calls itself recursively.
Otherwise, it returns an array with true, false, false for any key with the name propName.
The .reduce then rolls up the array through an or statement.
function deepCheck(obj,propName) {
if obj.hasOwnProperty(propName) { // Performance improvement (thanks to #nem's solution)
return true;
}
return Object.keys(obj) // Turns keys of object into array of strings
.map(prop => { // Loop over the array
if (typeof obj[prop] == 'object') { // If property is object,
return deepCheck(obj[prop],propName); // call recursively
} else {
return (prop == propName); // Return true or false
}
}) // The result is an array like [false, false, true, false]
.reduce(function(previousValue, currentValue, index, array) {
return previousValue || currentValue;
} // Do an 'or', or comparison of everything in the array.
// It returns true if at least one value is true.
)
}
deepCheck(object,'value'); // === true
PS: nem035's answer showed how it could be more performant: his solution breaks off at the first found 'value.'
My approach would be using try/catch blocks. Because I don't like to pass deep property paths in strings. I'm a lazy guy who likes autocompletion :)
JavaScript objects are evaluated on runtime. So if you return your object statement in a callback function, that statement is not going to be evaluated until callback function is invoked.
So this function just wraps the callback function inside a try catch statement. If it catches the exception returns false.
var obj = {
innerObject: {
deepObject: {
value: 'Here am I'
}
}
};
const validate = (cb) => {
try {
return cb();
} catch (e) {
return false;
}
}
if (validate(() => obj.innerObject.deepObject.value)) {
// Is going to work
}
if (validate(() => obj.x.y.z)) {
// Is not going to work
}
When it comes to performance, it's hard to say which approach is better.
On my tests if the object properties exist and the statement is successful I noticed using try/catch can be 2x 3x times faster than splitting string to keys and checking if keys exist in the object.
But if the property doesn't exist at some point, prototype approach returns the result almost 7x times faster.
See the test yourself: https://jsfiddle.net/yatki/382qoy13/2/
You can also check the library I wrote here: https://github.com/yatki/try-to-validate
I use try-catch:
var object = {
innerObject:{
deepObject:{
value:'Here am I'
}
}
};
var object2 = {
a: 10
}
let exist = false, exist2 = false;
try {
exist = !!object.innerObject.deepObject.value
exist2 = !!object2.innerObject.deepObject.value
}
catch(e) {
}
console.log(exist);
console.log(exist2);
Try this nice and easy solution:
public hasOwnDeepProperty(obj, path)
{
for (var i = 0, path = path.split('.'), len = path.length; i < len; i++)
{
obj = obj[path[i]];
if (!obj) return false;
};
return true;
}
In case you are writing JavaScript for Node.js, then there is an assert module with a 'deepEqual' method:
const assert = require('assert');
assert.deepEqual(testedObject, {
innerObject:{
deepObject:{
value:'Here am I'
}
}
});
I have created a very simple function for this using the recursive and happy flow coding strategy. It is also nice to add it to the Object.prototype (with enumerate:false!!) in order to have it available for all objects.
function objectHasOwnNestedProperty(obj, keys)
{
if (!obj || typeof obj !== 'object')
{
return false;
}
if(typeof keys === 'string')
{
keys = keys.split('.');
}
if(!Array.isArray(keys))
{
return false;
}
if(keys.length == 0)
{
return Object.keys(obj).length > 0;
}
var first_key = keys.shift();
if(!obj.hasOwnProperty(first_key))
{
return false;
}
if(keys.length == 0)
{
return true;
}
return objectHasOwnNestedProperty(obj[first_key],keys);
}
Object.defineProperty(Object.prototype, 'hasOwnNestedProperty',
{
value: function () { return objectHasOwnNestedProperty(this, ...arguments); },
enumerable: false
});
NB: The material in the subsection titled Background is not essential. The full description of the question is fully contained in the preceding paragraphs.
I'd like to implement a universal, lightweight, and "unobtrusive" way to "tag" arbitrary objects.
More specifically, I want to define the equivalent of the (abstract) functions tag, isTagged, and getTagged, such that:
isTagged(t) is true if and only if t was the value returned by tag(o), for some object o;
getTagged(tag(o)) is identical to o, for every object o;
if t = tag(o), then tag(t) should be identical to t;
with the exception of the behaviors described in (1), (2), and (3) above, and strict identity tests involving ===, tag(o) and o should behave the same way.
[EDIT: One further requirement is that the implementation should not modify the Object class, nor any other standard class, in any way.]
For example:
>>> isTagged(o = "foo")
false
>>> isTagged(t = tag(o))
true
>>> getTagged(t) === o
true
>>> tag(t) === t
true
>>> t.length
3
>>> t.toUpperCase()
"FOO"
Below I give my best shot at solving this problem. It is (almost) universal, but, as it will soon be clear, it is anything but lightweight!!! (Also, it falls rather short of fully satisfying requirement 4 above, so it is not as "unobtrusive" as I'd like. Moreover, I have serious doubts as to its "semantic correctness".)
This solution consists of wrapping the object o to be tagged with a "proxy object" p, and copying all the properties of o (whether "owned" or "inherited") to p.
My question is:
is it possible to achieve the specifications given above without having to copy all the properties of the tagged object?
Background
Here's the implementation alluded to above. It relies on the utility function getProperties, whose definition (FWIW) is given at the very end.
function Proxy (o) { this.__obj = o }
function isTagged(t) {
return t instanceof Proxy;
}
function getTagged(t) {
return t.__obj;
}
var tag = (function () {
function _proxy_property(o, pr) {
return (typeof pr === "function")
? function () { return pr.apply(o, arguments) }
: pr;
}
return function (o) {
if (isTagged(o)) return o;
if (typeof o.__obj !== "undefined") {
throw TypeError('object cannot be proxied ' +
'(already has an "__obj" property)');
}
var proxy = new Proxy(o);
var props = getProperties(o); // definition of getProperties given below
for (var i = 0; i < props.length; ++i) {
proxy[props[i]] = _proxy_property(o, o[props[i]]);
}
return proxy;
}
})();
This approach, ham-fisted though it is, at least seems to work:
// requirement 1
>>> isTagged(o = "foo")
false
>>> isTagged(p = tag(o))
true
// requirement 2
>>> getTagged(p) === o
true
// requirement 3
>>> tag(p) === p
true
// requirement 4
>>> p.length
3
>>> p.toUpperCase()
"FOO"
...well, almost; requirement (4) is not always satisfied:
>>> o == "foo"
true
>>> p == "foo"
false
>>> o == o
true
>>> p == o
false
FWIW, here's the definition of the function getProperties, which is used by the tag function. Criticisms welcome. (WARNING: I'm a completely clueless JS noob who doesn't know what he's doing! Use this function at your own risk!)
function getProperties(o) {
var seen = {};
function _properties(obj) {
var ret = [];
if (obj === null) {
return ret;
}
try {
var ps = Object.getOwnPropertyNames(obj);
}
catch (e if e instanceof TypeError &&
e.message === "obj is not an object") {
return _properties(obj.constructor);
}
for (var i = 0; i < ps.length; ++i) {
if (typeof seen[ps[i]] === "undefined") {
ret.push(ps[i]);
seen[ps[i]] = true;
}
}
return ret.concat(_properties(Object.getPrototypeOf(obj)));
}
return _properties(o);
}
I think you're overcomplicating all of this. There's no reason you need to store the tag on the object itself. If you create a separate object that uses the object's pointer as a key, not only will you conserve space, but you'll prevent any unintentional collisions should the arbitrary object happen to have a property named "_tagged".
var __tagged = {};
function tag(obj){
__tagged[obj] = true;
return obj;
}
function isTagged(obj){
return __tagged.hasOwnProperty(obj);
}
function getTagged(obj){
if(isTagged(obj)) return obj;
}
== EDIT ==
So I decided to take a minute to create a more robust tagging system. This is what I've created.
var tag = {
_tagged: {},
add: function(obj, tag){
var tags = this._tagged[obj] || (this._tagged[obj] = []);
if(tag) tags.push(tag);
return obj;
},
remove: function(obj, tag){
if(this.isTagged(obj)){
if(tag === undefined) delete this._tagged[obj];
else{
var idx = this._tagged[obj].indexOf(tag);
if(idx != -1) this._tagged[obj].splice(idx, 1);
}
}
},
isTagged: function(obj){
return this._tagged.hasOwnProperty(obj);
},
get: function(tag){
var objects = this._tagged
, list = []
;//var
for(var o in objects){
if(objects.hasOwnProperty(o)){
if(objects[o].indexOf(tag) != -1) list.push(o);
}
}
return list;
}
}
Not only can you tag an object, but you can actually specify different types of tags and retrieve objects with specific tags in the form of a list. Let me give you an example.
var a = 'foo'
, b = 'bar'
, c = 'baz'
;//var
tag.add(a);
tag.add(b, 'tag1');
tag.add(c, 'tag1');
tag.add(c, 'tag2');
tag.isTagged(a); // true
tag.isTagged(b); // true
tag.isTagged(c); // true
tag.remove(a);
tag.isTagged(a); // false
tag.get('tag1'); // [b, c]
tag.get('tag2'); // [c]
tag.get('blah'); // []
tag.remove(c, 'tag1');
tag.get('tag1'); // [b]
You're over complicating it :
var tag = function(o) {
Object.defineProperty(o, '__tagged', {
enumerable: false,
configurable: false,
writable: false,
value: "static"
});
return o;
}
var isTagged = function(o) {
return Object.getOwnPropertyNames(o).indexOf('__tagged') > -1;
}
I have a function that checks to see whether or not a request has any queries, and does different actions based off that. Currently, I have if(query) do this else something else. However, it seems that when there is no query data, I end up with a {} JSON object. As such, I need to replace if(query) with if(query.isEmpty()) or something of that sort. Can anybody explain how I could go about doing this in NodeJS? Does the V8 JSON object have any functionality of this sort?
You can use either of these functions:
// This should work in node.js and other ES5 compliant implementations.
function isEmptyObject(obj) {
return !Object.keys(obj).length;
}
// This should work both there and elsewhere.
function isEmptyObject(obj) {
for (var key in obj) {
if (Object.prototype.hasOwnProperty.call(obj, key)) {
return false;
}
}
return true;
}
Example usage:
if (isEmptyObject(query)) {
// There are no queries.
} else {
// There is at least one query,
// or at least the query object is not empty.
}
You can use this:
var isEmpty = function(obj) {
return Object.keys(obj).length === 0;
}
or this:
function isEmpty(obj) {
return !Object.keys(obj).length > 0;
}
You can also use this:
function isEmpty(obj) {
for(var prop in obj) {
if(obj.hasOwnProperty(prop))
return false;
}
return true;
}
If using underscore or jQuery, you can use their isEmpty or isEmptyObject calls.
Object.keys(myObj).length === 0;
As there is need to just check if Object is empty it will be better to directly call a native method Object.keys(myObj).length which returns the array of keys by internally iterating with for..in loop.As Object.hasOwnProperty returns a boolean result based on the property present in an object which itself iterates with for..in loop and will have time complexity O(N2).
On the other hand calling a UDF which itself has above two implementations or other will work fine for small object but will block the code which will have severe impact on overall perormance if Object size is large unless nothing else is waiting in the event loop.
If you have compatibility with Object.keys, and node does have compatibility, you should use that for sure.
However, if you do not have compatibility, and for any reason using a loop function is out of the question - like me, I used the following solution:
JSON.stringify(obj) === '{}'
Consider this solution a 'last resort' use only if must.
See in the comments "there are many ways in which this solution is not ideal".
I had a last resort scenario, and it worked perfectly.
My solution:
let isEmpty = (val) => {
let typeOfVal = typeof val;
switch(typeOfVal){
case 'object':
return (val.length == 0) || !Object.keys(val).length;
break;
case 'string':
let str = val.trim();
return str == '' || str == undefined;
break;
case 'number':
return val == '';
break;
default:
return val == '' || val == undefined;
}
};
console.log(isEmpty([1,2,4,5])); // false
console.log(isEmpty({id: 1, name: "Trung",age: 29})); // false
console.log(isEmpty('TrunvNV')); // false
console.log(isEmpty(8)); // false
console.log(isEmpty('')); // true
console.log(isEmpty(' ')); // true
console.log(isEmpty([])); // true
console.log(isEmpty({})); // true
const isEmpty = (value) => (
value === undefined ||
value === null ||
(typeof value === 'object' && Object.keys(value).length === 0) ||
(typeof value === 'string' && value.trim().length === 0)
)
module.exports = isEmpty;
This question already has answers here:
How to check if it's a string or json [duplicate]
(5 answers)
Closed 8 years ago.
How do I know if a variable is JSON or if it is something else? Is there a JQuery function or something I can use to figure this out?
Based on your comments, it sounds like you don't want to know whether a string is valid JSON, but rather whether an object could be successfully encoded as JSON (e.g. doesn't contain any Date objects, instances of user-defined classes, etc.).
There are two approaches here: try to analyze the object and its "children" (watch out for recursive objects) or suck-it-and-see. If you have a JSON encoder on hand (JSON.stringify in recent browsers or a plugin such as jquery-json), the latter is probably the simpler and more robust approach:
function canJSON(value) {
try {
JSON.stringify(value);
return true;
} catch (ex) {
return false;
}
}
Analyzing an object directly requires that you be able to tell whether it is a "plain" object (i.e. created using an object literal or new Object()), which in turn requires you be able to get its prototype, which isn't always straightforward. I've found the following code to work in IE7, FF3, Opera 10, Safari 4, and Chrome (and quite likely other versions of those browsers, which I simply haven't tested).
var getPrototypeOf;
if (Object.getPrototypeOf) {
getPrototypeOf = Object.getPrototypeOf;
} else if (typeof ({}).__proto__ === "object") {
getPrototypeOf = function(object) {
return object.__proto__;
}
} else {
getPrototypeOf = function(object) {
var constructor = object.constructor;
if (Object.prototype.hasOwnProperty.call(object, "constructor")) {
var oldConstructor = constructor; // save modified value
if (!(delete object.constructor)) { // attempt to "unmask" real constructor
return null; // no mask
}
constructor = object.constructor; // obtain reference to real constructor
object.constructor = oldConstructor; // restore modified value
}
return constructor ? constructor.prototype : null;
}
}
// jQuery.isPlainObject() returns false in IE for (new Object())
function isPlainObject(value) {
if (typeof value !== "object" || value === null) {
return false;
}
var proto = getPrototypeOf(value);
// the prototype of simple objects is an object whose prototype is null
return proto !== null && getPrototypeOf(proto) === null;
}
var serializablePrimitives = { "boolean" : true, "number" : true, "string" : true }
function isSerializable(value) {
if (serializablePrimitives[typeof value] || value === null) {
return true;
}
if (value instanceof Array) {
var length = value.length;
for (var i = 0; i < length; i++) {
if (!isSerializable(value[i])) {
return false;
}
}
return true;
}
if (isPlainObject(value)) {
for (var key in value) {
if (!isSerializable(value[key])) {
return false;
}
}
return true;
}
return false;
}
So yeah… I'd recommend the try/catch approach. ;-)
function isJSON(data) {
var isJson = false
try {
// this works with JSON string and JSON object, not sure about others
var json = $.parseJSON(data);
isJson = typeof json === 'object' ;
} catch (ex) {
console.error('data is not JSON');
}
return isJson;
}
You can use [json2.js] from Douglas Crockfords JSON Github site to parse it.
JSON is an encoding method not an internal variable type.
You might load in some text that is JSON encoded that javascript then uses to populate your variables. Or you might export a string that contains a JSON encoded dataset.
The only testing I've done is to check for a string, with and without double quotes, and this passes that test. http://forum.jquery.com/topic/isjson-str
Edit:
It looks like the latest Prototype has a new implementation similar to the one linked above. http://prototypejs.org/assets/2010/10/12/prototype.js
function isJSON() {
var str = this;
if (str.blank()) return false;
str = str.replace(/\\(?:["\\\/bfnrt]|u[0-9a-fA-F]{4})/g, '#');
str = str.replace(/"[^"\\\n\r]*"|true|false|null|-?\d+(?:\.\d*)?(?:[eE][+\-]?\d+)?/g, ']');
str = str.replace(/(?:^|:|,)(?:\s*\[)+/g, '');
return (/^[\],:{}\s]*$/).test(str);
}