28

How to know whether an object is array or not?

 var x=[];

console.log(typeof x);//output:"object"
alert(x);//output:[object Object]
console.log(x.valueOf())//output:<blank>? what is the reason here?
console.log([].toString()); also outputs <blank>     
Object.prototype.toString.call(x) output:[object Array] how?

since console.log([].toString()); outputs :blank

1st:

why i get blank at 2nd last statement?

2nd:

Is there a way to know exactly what an object is: Array or plain Object({}) without the help of their respective methods like x.join() indicates x is an Array,not in this way.

Actually,in jquery selection like $("p") returns jquery object so if i use

console.log(typeof $("p"));//output:"object

I just wanted to know the actual Name of the Object.Thats it.Thank u for u help

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1

6 Answers 6

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13

In pure JavaScript you can use the following cross browser approach:

if (Object.prototype.toString.call(x) === "[object Array]") {
    // is plain array
}

jQuery has special method for that:

if ($.isArray(x)) {
    // is plain array
}
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7 Comments

console.log([].valueOf())//output:<blank>? what is the reason here?
@Maizere Basically [].valueOf() returns [], and doesn't make any sense here.
@Maizere Glad it helped. FYI, jQuery has also $.isPlainObject() for objects check.
Object.prototype.toString.call(x) output:[object Array] how? since console.log([].toString()); outputs :blank
@Maizere Because Object.prototype.toString is not the same as Array.prototype.toString. The latter simply stringifies array, e.g. [1,2,3].toString() === "1,2,3".
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4

You can use instanceof. Here's some FireBug testing:

test1 = new Object();
test2 = new Array();
test3 = 123;

console.log(test1 instanceof Array); //false
console.log(test2 instanceof Array); //true
console.log(test3 instanceof Array); //false

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3 Comments

Maybe the downvoter would be kind enough to explain why the -1, for the sake of learning :)
Wasn't me (frankly I don't think this is wrong enough to deserve a downvote), but this fails in multi-DOM environments such as iframes and the like. See this article for more.
It is a simple and clean solution which works in my scenario. Tested on latest version of Chrome and Firefox. Thanks
2

Best practice is the invocation of Object.prototype.toString() on the target object, which displays the internal [[Class]] property name.

Object.prototype.toString.call( x ); // [object Array]

This has the adventage, that it works on any and every object, regardless of if you're working in a multi frame / window environment, which causes problems on using x instanceof Array.

Newer ES5 implementations, also give you the method Arrays.isArray(), which returns true or false.

Array.isArray( x ); // true

And last but not least, jQuery has its very own .isArray() method, which also returns a boolean

jQuery.isArray( x ); // true
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1

Simple: 

if( Object.prototype.toString.call( someVar ) === '[object Array]' ) {
    alert( 'Array!' );
}
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1

http://api.jquery.com/jQuery.isArray/

if($.isArray(x)){
  alert("isArray");
}
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0

I think you are searching for something like this:

if( Object.prototype.toString.call( someVar ) === '[object Array]' ) {
    alert( 'Array!' );
}

Hope this helps. A little to slow :P

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1 Comment

Yes, this has already been posted two or three times.

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