What is a JavaScript Array?

Question

I'm trying to understand what a JavaScript array is because traditional programming languages define an array as a contiguous area of storage that can be addressed using an offset.

Now, a normal JavaScript object can be addressed as:

myObj.myProperty = "my Value";

or

myObj["myProperty"] = "my Value";

So, a JavaScript array is simply using numbers instead of names in it's addressing:

myObj[0] = "my Value";
myObj.length // === 1

A JavaScript Array also has methods, such as slice(), and join().

Q: Is what I said so far true?

Slight correction on one point: "a JavaScript array is simply using numbers instead of names in it's addressing" -- it's actually still using strings. When you type myObj[0], it gets converted to myObj['0'] — user578895
– user578895, Commented Jun 22, 2011 at 19:05

user578895 · Accepted Answer · 2011-06-22 18:55:18Z

5

A JavaScript array is a hash object with array functions attached using Array.prototype. Put simply, this is an "Array" in JavaScript:

var x = {
    length : 3,
    '0'    : 'first',
    '1'    : 'second',
    '2'    : 'third'
};
x.__proto__ = Array.prototype;

All of the array functions only act on indexes, as you would expect, however you can also do anything to an array object that you would do to a general JS object:

ary.foo = 'bar';

answered Jun 22, 2011 at 18:55

user578895

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6 Comments

user578895 Over a year ago

@Neal - only because it's a syntax error in JS. x['0'] works fine

Naftali Over a year ago

@cwolves, yes i know that, but you stated that you van do the same operations as a normal object which you cannot.

user578895 Over a year ago

@Neal - yes, you can. You can't do x.0 on a generic object either :)

Naftali Over a year ago

@cwolves. yes but all of the indexes on an array object are usually numbers

user578895 Over a year ago

@Neal - they're always numbers. There's nothing you can do to a generic object that you can't do an array since Array inherits from Object. The fact that dot notation doesn't work on numbers doesn't negate that, it just means that you can't access numeric properties the same way.

|

Naftali · Accepted Answer · 2011-06-22 18:54:44Z

2

To a basic yes or no question: Yes all of what you said is true.

Here is a whole array tutorial

answered Jun 22, 2011 at 18:54

Naftali

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Comments

zellio · Accepted Answer · 2011-06-22 18:55:26Z

1

Javascript objects are associative arrays. Javascript has an Object called Array that has special methods for dealing with their data.

answered Jun 22, 2011 at 18:55

zellio

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1 Comment

user578895 Over a year ago

-1: very bad phrasing for newbies to JS. JS arrays are NOT associative arrays. When used as arrays, they act as normal indexed arrays. When used as an object they're associative. There are loads of arguments against using them as objects.

Ateş Göral · Accepted Answer · 2011-06-22 19:20:31Z

1

a good read ( that got me going at start ) Mastering Javascript Arrays

edited Jun 22, 2011 at 19:20

Ateş Göral

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answered Jun 22, 2011 at 18:57

Rafael Herscovici

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2 Comments

Phillip Senn Over a year ago

Thanks Ates! I'll look at it later tonight!

Rafael Herscovici Over a year ago

lol, you ment "Thanks Dementic" :D he just fixed a misspell of mine. XD

cirne100 · Accepted Answer · 2011-06-22 19:55:58Z

1

Any JavaScript array is an object that can use different objects* as keys, making it a hash.

*all objects different from strings will be converted to string [object Object], so they will act as the same key! (thanks to cwolves :)

edited Jun 22, 2011 at 19:55

answered Jun 22, 2011 at 19:05

cirne100

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3 Comments

cirne100 Over a year ago

@cwolves - any "non string" value different from null and undefined will be converted into a string because all object property names are strings!

user578895 Over a year ago

yes, I realize that, but saying that you can use "different objects as keys" implies that this will work as expected: var x={}, y={}, z={}; x[y] = 1; x[z] = 2;, but in reality you'd get x == {'[object Object]' : 2}. And FYI, null and undefined work too :)

nnnnnn Over a year ago

Note that you can define your own toString() method on your objects and then they will be usable as keys (assuming you come up with a meaningful way of providing uniqueness).

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