Distinguish between array and hash in javascript with typeof() [duplicate]

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Possible Duplicate:

In javascript how can we identify whether an object is a Hash or an Array?

In javascript

typeof([])

and

typeof({})

both return "object".

How can I reliably distinguish between an array and an associative array in Javascript?

I have thought of testing the object in question to see if it has the "length" attribute (indi开发者_如何学Gocating it would be an array), but what then the following would also be seen as an array:

{length:5}

---

Modern browsers have Array.isArray built in.

For older browsers, you can test for that function and add it when necessary.

if( typeof Array.isArray !== 'function' ) {
    Array.isArray = function( arr ) {
        return Object.prototype.toString.call( arr ) === '[object Array]';
    };
}

alert( Array.isArray( [] ) );

---

EDIT:

Array.isArray is part of ECMAScript 5:

15.4.3.2 Array.isArray ( arg )

The isArray function takes one argument arg, and returns the Boolean value true if the argument is an object whose class internal property is "Array"; otherwise it returns false. The following steps are taken:

1. If Type(arg) is not Object, return false.
2. If the value of the [[Class]] internal property of arg is "Array", then return true.
3. Return false.

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A good idea is, to check for the internal [[CClass]] value. To do that, you need to invoke Object.prototype.toString:

var toStr = Object.prototype.toString;

toStr.call([]);  // === [object Array]
toStr.call({});  // === [object Object]

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Associative arrays do not exist in Javascript.

An array can only have numeric keys. If you access a string key, you are in fact using a shortcut, which is exactly equivalent to the object notation.

http://www.quirksmode.org/js/associative.html

http://andrewdupont.net/2006/05/18/javascript-associative-arrays-considered-harmful/