How to match an empty dictionary in Javascript?

Question

From the node REPL thing,

> d = {}
{}
> d === {}
false
> d == {}
false

Given I have an empty dictionary, how do I make sure it is an empty dictionary ?

You might consider using a library such as [check-types](https://www.npmjs.com/package/check-types). In which case, you could use `check.emptyObject(d)`. — mareoraft, Oct 29 '15 at 00:36
Here is a more up-to-date answer: https://stackoverflow.com/questions/679915/how-do-i-test-for-an-empty-javascript-object — guettli, Nov 27 '19 at 15:08

score 124 · Accepted Answer · answered May 20 '11 at 13:35

124

function isEmpty(obj) {
  return Object.keys(obj).length === 0;
}

answered May 20 '11 at 13:35

Raynos

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Only in newer browsers. For the record, the keys property is only supported in IE >= 9 [reference](http://kangax.github.io/compat-table/es5/) – Nick Mitchell Dec 09 '14 at 04:52
6

I'd be amazed at JavaScript lacking this basic functionality, if I weren't so used to it by now. – Teekin Oct 15 '19 at 11:29
Here is a more up-to-date answer: https://stackoverflow.com/questions/679915/how-do-i-test-for-an-empty-javascript-object – guettli Nov 27 '19 at 15:08

Gumbo · Answer 2 · 2011-05-20T13:54:07.730

19

You could extend Object.prototype with this isEmpty method to check whether an object has no own properties:

Object.prototype.isEmpty = function() {
    for (var prop in this) if (this.hasOwnProperty(prop)) return false;
    return true;
};

edited May 20 '11 at 13:54

answered May 20 '11 at 13:35

Gumbo

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Wow ..I find it rather interesting that javascript lacks this "basic" functionality – harijay Oct 12 '11 at 22:28
2

Extending the Object.prototype can create problems iterating over the object later http://yuiblog.com/blog/2006/09/26/for-in-intrigue/ – Camilo Sanchez Jun 12 '14 at 14:22
1

This interferes with jquery – Rubber Duck Dec 24 '14 at 10:14
test in react js, but output `Object.prototype.isEmpty: this= undefined`, so not work, how fix this? – crifan Jul 31 '18 at 02:53

stroz · Answer 3 · 2016-02-10T19:58:20.643

15

How about using jQuery?

$.isEmptyObject(d)

edited Feb 10 '16 at 19:58

answered Oct 28 '13 at 22:08

stroz

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score 10 · Answer 4 · answered May 20 '11 at 13:32

10

Since it has no attributes, a for loop won't have anything to iterate over. To give credit where it's due, I found this suggestion here.

function isEmpty(ob){
   for(var i in ob){ return false;}
  return true;
}

isEmpty({a:1}) // false
isEmpty({}) // true

answered May 20 '11 at 13:32

David Ruttka

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I would create a count(obj) function and isEmpty would eval if count equals 0. – Matías Fidemraizer May 20 '11 at 13:34
5

You might want to check for `obj.hasOwnProperty(i)` before returning false. This filters out properties inherited through the prototype chain. – Elian Ebbing May 20 '11 at 13:36

score 9 · Answer 5 · answered Aug 05 '12 at 14:27

This is what jQuery uses, works just fine. Though this does require the jQuery script to use isEmptyObject.

isEmptyObject: function( obj ) {
    for ( var name in obj ) {
        return false;
    }
    return true;
}

//Example
var temp = {};
$.isEmptyObject(temp); // returns True
temp ['a'] = 'some data';
$.isEmptyObject(temp); // returns False

If including jQuery is not an option, simply create a separate pure javascript function.

function isEmptyObject( obj ) {
    for ( var name in obj ) {
        return false;
    }
    return true;
}

//Example
var temp = {};
isEmptyObject(temp); // returns True
temp ['b'] = 'some data';
isEmptyObject(temp); // returns False

score 5 · Answer 6 · answered Jul 27 '14 at 13:27

5

I'm far from a JavaScript scholar, but does the following work?

if (Object.getOwnPropertyNames(d).length == 0) {
   // object is empty
}

It has the advantage of being a one line pure function call.

answered Jul 27 '14 at 13:27

Steve Bennett

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cool solution! it is actually the only one without loops and without invoking third-party libraries – Antonio Ragagnin Dec 27 '15 at 13:18

score 1 · Answer 7 · answered Dec 23 '15 at 11:24

1

var SomeDictionary = {};
if(jQuery.isEmptyObject(SomeDictionary))
// Write some code for dictionary is empty condition
else
// Write some code for dictionary not empty condition

This Works fine.

answered Dec 23 '15 at 11:24

VAMSHI PAIDIMARRI

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score 1 · Answer 8 · answered Jan 05 '17 at 23:49

1

If performance isn't a consideration, this is a simple method that's easy to remember:

JSON.stringify(obj) === '{}'

Obviously you don't want to be stringifying large objects in a loop, though.

answered Jan 05 '17 at 23:49

Steve Bennett

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score 1 · Answer 9 · edited May 23 '17 at 11:47

1

You'd have to check that it was of type 'object' like so:

(typeof(d) === 'object')

And then implement a short 'size' function to check it's empty, as mentioned here.

edited May 23 '17 at 11:47

Community

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answered May 20 '11 at 13:33

chrisfrancis27

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score 0 · Answer 10 · edited Oct 27 '12 at 05:54

0

If you try this on Node.js use this snippet, based on this code here

Object.defineProperty(Object.prototype, "isEmpty", {
    enumerable: false,
    value: function() {
            for (var prop in this) if (this.hasOwnProperty(prop)) return false;
            return true;
        }
    }
);

edited Oct 27 '12 at 05:54

Peter O.

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answered Jan 08 '12 at 17:31

arbyter

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How to match an empty dictionary in Javascript?

10 Answers10