How to check if object has any properties in JavaScript?

Question

Assuming I declare

var ad = {}; 

How can I check whether this object will contain any user-defined properties?

Answer 1

How about this?

var obj = {},
var isEmpty = !obj;
var hasContent = !!obj

Answer 2

Very late answer, but this is how you could handle it with prototypes.

Array.prototype.Any = function(func) {
    return this.some(func || function(x) { return x });
}

Object.prototype.IsAny = function() {
    return Object.keys(this).Any();
}

Answer 3

You can use the following:

Double bang !! property lookup

var a = !![]; // true
var a = !!null; // false

hasOwnProperty This is something that I used to use:

var myObject = {
  name: 'John',
  address: null
};
if (myObject.hasOwnProperty('address')) { // true
  // do something if it exists.
}

However, JavaScript decided not to protect the method’s name, so it could be tampered with.

var myObject = {
  hasOwnProperty: 'I will populate it myself!'
};

prop in myObject

var myObject = {
  name: 'John',
  address: null,
  developer: false
};
'developer' in myObject; // true, remember it's looking for exists, not value.

typeof

if (typeof myObject.name !== 'undefined') {
  // do something
}

However, it doesn't check for null.

I think this is the best way.

in operator

var myObject = {
  name: 'John',
  address: null
};

if('name' in myObject) {
  console.log("Name exists in myObject");
}else{
  console.log("Name does not exist in myObject");
}

result:

Name exists in myObject

Here is a link that goes into more detail on the in operator: Determining if an object property exists

Answer 4

When sure that the object is a user-defined one, the easiest way to determine if UDO is empty, would be the following code:

isEmpty=
/*b.b Troy III p.a.e*/
function(x,p){for(p in x)return!1;return!0};

Even though this method is (by nature) a deductive one, - it's the quickest, and fastest possible.

a={};
isEmpty(a) >> true

a.b=1
isEmpty(a) >> false 

p.s.: !don't use it on browser-defined objects.

Answer 5

You can loop over the properties of your object as follows:

for(var prop in ad) {
    if (ad.hasOwnProperty(prop)) {
        // handle prop as required
    }
}

It is important to use the hasOwnProperty() method, to determine whether the object has the specified property as a direct property, and not inherited from the object's prototype chain.

Edit

From the comments: You can put that code in a function, and make it return false as soon as it reaches the part where there is the comment

Performance Test

Test Of Object.Keys vs For..In When testing for any properties

Answer 6

for (var hasProperties in ad) break;
if (hasProperties)
    ... // ad has properties

If you have to be safe and check for Object prototypes (these are added by certain libraries and not there by default):

var hasProperties = false;
for (var x in ad) {
    if (ad.hasOwnProperty(x)) {
        hasProperties = true;
        break;
    }
}
if (hasProperties)
    ... // ad has properties