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Are Javascript arrays primitives? Strings? Objects?

Are arrays merely objects in disguise? Why/why not? In what way(s) are they (such/not)?

I have always thought of arrays and objects in JS as essentially the same, primarily because accessing them is identical.

var obj = {'I': 'me'};
var arr = new Array();
arr['you'] = 'them';
console.log(obj.I);
console.log(arr.you);
console.log(obj['I']);
console.log(arr['you']);

Am I mislead/mistaken/wrong? What do I need to know about JS literals, primitives, and strings/objects/arrays/etc...?

Are arrays/objects merely strings in disguise? Why/why not? In what way(s) are they (such/not)?

Answer*

In JavaScript you have a few types, _everything_ else is an object. The types in JavaScript are: boolean, number, and string. There are also two special values, "null" and "undefined".

So the quest "is a JavaScript array an object?" is slightly ambiguous. Yes, a JavaScript array is an "object" but it is not an instance of "Object". A JavaScript array is an instance of "Array". Although, all objects inherit from Object; you can view the inheritance chain on [the MDC](https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Array/prototype). Additionally, arrays have slightly different properties than an object. Arrays have the `.length` property. They also have the `.slice()`, `.join()`, etc methods.

Douglas Crockford provides a nice [survey][1] of the language's features. His survey discusses the differences you are asking about. Additionally, you can read more about the [difference between literals and constructors][2] in question #4559207.


 [1]: http://javascript.crockford.com/survey.html
 [2]: https://stackoverflow.com/questions/4559207/difference-between-a-constructor-and-an-object

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Now see, this jibes with what I understand. The three types. But how to explain Object, in which everything else is constructed, except arrays? Are we only talking about default method prototypes? "Yes, a JavaScript array is an "object" but it is not an instance of "Object" This gets to the heart of what I am inquiring about.

Jared Farrish
– Jared Farrish

2011年02月19日 03:04:25 +00:00
Commented Feb 19, 2011 at 3:04
And yes, Crockford is the reason Javascript is taken seriously, IMO. He's been organizing sanity on the Javascript front for too long to remember (at least since 2004, earlier?).

Jared Farrish
– Jared Farrish

2011年02月19日 03:07:34 +00:00
Commented Feb 19, 2011 at 3:07
@Jared You know Crockford but haven't watched his most fundamental JavaScript video series? Go watch it now! :)

Šime Vidas
– Šime Vidas

2011年02月19日 03:35:40 +00:00
Commented Feb 19, 2011 at 3:35
@jsummers - So Arrays are fancy character arrays with self-defined special methods?

Jared Farrish
– Jared Farrish

2011年02月19日 03:38:05 +00:00
Commented Feb 19, 2011 at 3:38
@Šime Vidas - Yeah, I know. Crockford is god. The point here is to extract as much meaning as possible, as opposed to my own stochastic learning processes. I want there to be a meaning that would have been meaningful for me, back then (Thanks Thau!).

Jared Farrish
– Jared Farrish

2011年02月19日 03:41:19 +00:00
Commented Feb 19, 2011 at 3:41

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Are Javascript arrays primitives? Strings? Objects?

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