How can I tell if it is an object or an array?

Question

I want to know the type of the variable put in the function. So, I used typeof and like this:

randomFunctionName: function(obj){
    switch(typeof obj){
        case "object":
           //Something
        case "text":
            //Something else
    }
}

But the problem is, I can't tell if obj is an array or an object, since

typeof [] === "object"  //true
typeof {} === "object"  //true

So, how I can I separate them? Is there any difference between them?

I think this is a common advanced topic, such as here: http://stackoverflow.com/questions/4587061/how-to-determine-if-object-is-in-array — Marc, Apr 29 '12 at 00:11
Another example is http://stackoverflow.com/questions/6844981/distinguish-between-array-and-hash-in-javascript-with-typeof — Geoff Adams, Apr 29 '12 at 00:11
Or here: http://stackoverflow.com/questions/5336090/is-this-an-acceptable-way-to-determine-if-an-object-is-an-array-in-javascript — Marc, Apr 29 '12 at 00:12
How can you find those links? I searched for a few times and what I found is `nothing` related. — Derek 朕會功夫, Apr 29 '12 at 00:13

score 6 · Accepted Answer · answered Apr 29 '12 at 00:13

6

An array is an object. You can test if an object is an array as follows:

Object.prototype.toString.apply(value) === '[object Array]';

You can wrap this up into a function as follows:

function isArray(a)
{
    return Object.prototype.toString.apply(a) === '[object Array]';
}

answered Apr 29 '12 at 00:13

Joe Alfano

10,149
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2

Is `[object Array]` the same in every browser? – Derek 朕會功夫 Apr 29 '12 at 00:18
1

Yes, this will work for any browser that is ECMAScript compliant, which should be all browsers. – Joe Alfano Apr 29 '12 at 00:29

score 4 · Answer 2 · answered Apr 29 '12 at 00:14

4

check the constructor:

[].constructor == Array  //true
{}.constructor == Object  //true

answered Apr 29 '12 at 00:14

Dr.Molle

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`{}.constructor` --> `SyntaxError: Unexpected token .` – Derek 朕會功夫 Apr 29 '12 at 00:15
I see the image but I don't get the error in chrome(the image looks like chrome) – Dr.Molle Apr 29 '12 at 00:29
I am using Chrome 20.0.1115.1 Do you think it is a bug of Chrome or did I do something wrong? – Derek 朕會功夫 Apr 29 '12 at 00:30
The latest version I can get (winXP) is 18.0.1025.162 m and i don't get any error. chrome19 is BETA and chrome20 is dev, so I don't have do care about them because they don't have to be stable. – Dr.Molle Apr 29 '12 at 00:37
I am actually using the dev channel, but I don't think that will affect JavaScript? – Derek 朕會功夫 Apr 29 '12 at 00:42

score 1 · Answer 3 · answered Feb 12 '14 at 12:46

Since ECMAScript 5 you can use the native method:

Array.isArray( maybeArray );

If compatibility is of concern you can use Underscore.js or jQuery:

_.isArray( maybeArray ); // will use the native method if available
$.isArray( maybeArray );

This kind of utility is also present in AngularJS.

score 0 · Answer 4 · answered Apr 29 '12 at 00:12

0

This is pretty simple. Try something like

var to = {}.toString;
alert(to.call([])); //[object Array]
alert(to.call({})); //[object Object]

answered Apr 29 '12 at 00:12

Martin.

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How can I tell if it is an object or an array?

4 Answers4