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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)?

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  • "arrays are just like regular objects" - That's interesting. Arrays, other than a few methods decorating them, are objects, and objects are...? Especially if an associative array is really just "cast" into an object magically. Are associative arrays still arrays in this sense? (I apologize in advance if my use of cast is incorrect.) Commented Feb 19, 2011 at 2:59
  • @Jared In JavaScript, all objects are associative arrays. Commented Feb 19, 2011 at 3:04
  • @Šime Vidas - So why have an array object? I'm just wondering, is it to expose the .length property? They seem to be so similar. Commented Feb 19, 2011 at 3:06
  • 1
    @Jared Use arrays when the member names would be sequential integers. Use objects when the member names are arbitrary strings or names. Commented Feb 19, 2011 at 3:11
  • 1
    @Jared 1. JavaScript does not convert arrays into objects. Arrays can contain non-indexed properties just like objects. In fact, arrays can do everything that regular objects can do (and a few things more). 2. In the realm of JavaScript, there exist only objects and primitive values. Only those two things. And objects have the characteristics of associative arrays. 3. BTW, I found a good definition of an object in JavaScript: An object is a collection of properties. Commented Feb 19, 2011 at 4:03

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