How can I find out if an object has contents?

Question

If I set a variable like this:

var a = {};

Check if it has any contents

var b = { x: 1 }

Check if it has any contents

var c = { y: null }

I think the test (a) will not work as it is not null. So how can I check if it has some contents if I do not know in advance what the contents are? In this case I want variables b and c to show up as having contents.

score 1 · Answer 1 · answered Jun 04 '14 at 03:03

1

function isEmpty(input)
{
    var result = true;


    for(item in input)
        result = false;

    return result;
}

answered Jun 04 '14 at 03:03

John

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score 1 · Answer 2 · answered Jun 04 '14 at 03:05

1

A little wordy, but this should work:

var hasProperties = false;
for(var prop in obj) {
    hasProperties = true;
    break;
}

answered Jun 04 '14 at 03:05

Allen G

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And for inhertied enumerable properties? – RobG Jun 04 '14 at 03:20
Inherited enumerable properties should be detected using this, which as I assume, is favorable behaviour for the OP. Though, according to the scenario of "if I set a variable like var a = {...}," inheritance should not be an issue. – Allen G Jun 04 '14 at 03:38
I guess it highlights the futility of a general purpose "is plain object" test, they all only work within a limited set of criteria. In the above, extending *Object.prototype* with an enumerable properties means that all objects "have contents". – RobG Jun 04 '14 at 08:40

xdazz · Accepted Answer · 2014-06-04T09:10:49.493

0

Below is a piece of code what jQuery does:

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

edited Jun 04 '14 at 09:10

answered Jun 04 '14 at 03:02

xdazz

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Should mention that [this doesn't work in old IE](http://stackoverflow.com/questions/891299/browser-native-json-support-window-json) (not a concern for most, but worth noting) – random_user_name Jun 04 '14 at 03:04
1

Functions don't get stringified into JSON – danronmoon Jun 04 '14 at 03:05
@xdazz— `JSON.stringify({foo:function(){}}) == '{}'` returns `true`. – RobG Jun 04 '14 at 08:45
@RobG Oh, that's true. – xdazz Jun 04 '14 at 09:10

score 0 · Answer 4 · answered Jun 04 '14 at 03:11

0

Try if(Object.keys(a).length).

answered Jun 04 '14 at 03:11

Kamrul

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score 0 · Answer 5 · answered Jun 04 '14 at 03:30

Lots of answers, but I guess you want to check for own properties of the object:

for (var p in obj) {
  if (obj.hasOwnProperty(p)) {
    // obj has at least one enumerable own property
  }
}

But note that in ES5, objects can be constructed with non–enumerable own properties:

function hasEnumerableOwnProperties(obj) {
  for (var p in obj) {
    if (obj.hasOwnProperty(p)) return true;
  }
  return false;
}

var obj = {}

Object.defineProperty(obj, 'foo', {enumerable:false, value:'foo'})

console.log(hasEnumerableOwnProperties(obj) + ':' + obj.foo); // false:foo

Javascript isn't designed to suit this kind of analysis, it's much better if you're after a particular property, feature or attribute to test for it specifically (i.e. use feature detection).

Don't try to infer some general behaviour based on a simple (often inconclusive) test (duck typing).

How can I find out if an object has contents?

5 Answers5