How do I determine if something is an Array or Object?

Question

Array and object are the only inputs . Is there a simple function that can determine whether a variable is an array or object?

have you checked this? - http://stackoverflow.com/questions/8834126/how-to-efficiently-check-if-variable-is-array-or-object-in-nodejs-v8 — Freddie Fabregas, Apr 16 '13 at 04:18
http://blog.niftysnippets.org/2010/09/say-what.html .. worth looking — alwaysLearn, Apr 16 '13 at 04:18

elclanrs · Accepted Answer · 2013-04-16T04:31:05.283

3

I suspect there are many other similar answers but this is one way:

if ({}.toString.call(obj) == '[object Object]') {
  // is an object
}

if ({}.toString.call(obj) == '[object Array]') {
  // is an array
}

This can be turned into a nifty function:

function typeOf(obj) {
  return {}.toString.call(obj).match(/\w+/g)[1].toLowerCase();
}

if (typeOf(obj) == 'array') ...

This works for any type:

if (typeOf(obj) == 'date') // is a date
if (typeOf(obj) == 'number') // is a number
...

edited Apr 16 '13 at 04:31

answered Apr 16 '13 at 04:17

elclanrs

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+1, but you should use `Object.prototype.toString` as the `toString` method of the global/window object may not produce an appropriate result. :-) – RobG Apr 16 '13 at 04:28
I guess it depends on how much browser support you need. This should work on modern browsers AFAIK. It defaults to `window.toString` which is an object. Otherwise I'd prefer `{}.toString`. But you're right. – elclanrs Apr 16 '13 at 04:29
In Firefox, `window.toString.call(obj)` returns `[xpconnect wrapped native prototype]`. Note that `window` is a host object so not bound to comply with rules for native objects. Also, the [global object](http://www.ecma-international.org/ecma-262/5.1/#sec-15.1) is not an instance of Object (it doesn't have a `[[Prototype]]` property defined by ECMA-262 either), it's a special object that exists before any other. – RobG Apr 16 '13 at 04:31
Just updated to use the proper (shorter) way that should work on all modern browsers. AFAIK only IE7- has problems that can be easily solved with `({}).toString`. I've been using `window.toString` without problems tho in browsers that I need to target, but I see the trouble. – elclanrs Apr 16 '13 at 04:34
I guess the last caveat is that this may not work with host objects, it may even throw an error, but it should be OK in the OP's case. – RobG Apr 16 '13 at 05:32

score 1 · Answer 2 · answered Apr 16 '13 at 04:21

1

(variable instanceof Array) will return true for arrays.

You could also use variable.isArray(), but this is not supported by older browsers.

answered Apr 16 '13 at 04:21

Christophe

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score 1 · Answer 3 · answered Apr 16 '13 at 04:21

You can use Array.isArray():

if(Array.isArray(myVar)) {
    // myVar is an array
} else {
    // myVar is not an array
}

As long as you know it will be one or the other you are set. Otherwise, combine this with typeof:

if(typeof myVar === "object") {
    if(Array.isArray(myVar)) {
        // myVar is an array
    } else {
        // myVar is a non-array object
    }
}

score 1 · Answer 4 · answered Apr 16 '13 at 04:21

1

First check if it is an instanceof Array and then if it of object type.

if(variable instanceof Array)
{
//this is an array. This needs to the first line to be checked 
//as an array instanceof Object is also true

}
else if(variable instanceof Object)
{
//it is an object
}

answered Apr 16 '13 at 04:21

PSL

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Fails if the object is passed across a frame as it will be created from a different instance of Array and Object. – RobG Apr 16 '13 at 04:26

How do I determine if something is an Array or Object?

4 Answers4