Use of {} in JavaScript?

Question

Very simple question but I'm quite new to JS and this is not easy to search.

If I see a line like this:

var colours = {}, r, g, b;

I get that it's just a declaration for 3 vars, but what does the {} bit mean? I can't see anywhere that gives me an idea as to what this is declaring?

Thanks!

possible duplicate of [What do curly braces in javascript mean?](http://stackoverflow.com/questions/9699064/what-do-curly-braces-in-javascript-mean) — Felix Kling, May 11 '12 at 12:54

score 6 · Answer 1 · answered May 11 '12 at 12:53

6

It declares new object and equivalent to new Object();

answered May 11 '12 at 12:53

antyrat

27,479
9
75
76

score 4 · Accepted Answer · answered May 11 '12 at 13:02

4

 var colours = {}, r, g, b;

This declares 4 variables which is the same as

   var colors = {}; // this is an empty object like, var colors = new Object();
   var r; // undefined
   var g; // undefined
   var b; // undefined

answered May 11 '12 at 13:02

kamui

3,339
3
26
44

score 2 · Answer 3 · answered May 11 '12 at 12:52

2

It means that colours is going to be an object.

answered May 11 '12 at 12:52

ShaneBlake

11,056
2
26
43

score 2 · Answer 4 · answered May 11 '12 at 12:54

2

{} declares an object, with no members. Like an empty data container. [] would declare an empty array.

Arrays have number indexes (and a few handy methods) and objects can have string indexes (but lack the methods of an array)

answered May 11 '12 at 12:54

K..

4,044
6
40
85

2

Fun fact: Even arrays are objects in JavaScript. – Chris Sobolewski May 11 '12 at 12:55
3

They don't have "string indexes" but "properties". The `[]` syntax is just another way to access their properties (and the only proper way to access a property with a non-fixed name, e.g. `foo['bar' + x]`) – ThiefMaster May 11 '12 at 12:55

score 2 · Answer 5 · answered May 11 '12 at 12:55

2

It's a declaration of four variables, not three. One is called colours and is initialized to {}. The others are called r, g, and b, and their initial values are undefined. {} is an empty object literal.

answered May 11 '12 at 12:55

Gareth McCaughan

19,888
1
41
62

score 1 · Answer 6 · answered May 11 '12 at 12:53

1

It's declaring an empty object literal.

answered May 11 '12 at 12:53

Rob

12,659
4
39
56

score 1 · Answer 7 · answered May 11 '12 at 12:53

It initializes colors with a new, empty object.

While objects in JavaScript can have methods, too, they are often used as associative arrays, which is pretty likely in this case (assumption based on the name and the fact that it's initialized without any properties).

Use of {} in JavaScript?

7 Answers7