what's the difference between { } and [ ] in javascript

Question

Im coding a BackboneJS example app with the following syntax

<script type="text/javascript">
    var object = [];

    _.extend(object, Backbone.Events);
     object.on("alert", function(msg)
    {
       console.log("Your name is: "+msg);
     });

    object.trigger("alert","Sarah");
</script>

I noticed that the app works if the variable is defined like this

var object = {}

is there any difference between the two?

oh I found this example http://eloquentjavascript.net/chapter4.html

{} is used to pass JSON like this

var cat = {colour: "grey", name: "Spot", size: 46};

[] is just an array

var cat = ["color one", "color two", "color three"];

thanks

Well {} isn't strictly used for JSON. It's used to instantiate javascript objects in general but I understand the confusion. — spassvogel, Feb 20 '14 at 16:00
@NiettheDarkAbsol: Not exactly everything. Both are objects (though one is a special `Array` object). — Bergi, Feb 20 '14 at 16:02
so what exactly would be the difference between var object = {} and var object = null aren't they both empty variables? since a variable is an object too, im confused =/ — Gabriel ThaKid, Feb 20 '14 at 16:04

score 4 · Accepted Answer · answered Feb 20 '14 at 15:51

4

[] is an array literal:

An array literal is a list of zero or more expressions, each of which represents an array element, enclosed in square brackets ([]).

{} is an object literal:

An object literal is a list of zero or more pairs of property names and associated values of an object, enclosed in curly braces ({}).

answered Feb 20 '14 at 15:51

CD..

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all answers were good, but this one is the best – Gabriel ThaKid Feb 20 '14 at 16:09

spassvogel · Answer 2 · 2014-02-20T15:55:42.353

In short: [] is an array and {} is an object.

[] is shorthand for new Array()
{} is shorthand for new Object()

Basically, an Array is also an Object, but with added functionality. It is however, discouraged to use the Array as a hashmap (so, using strings as accessors).

Also, in your code the Array seems to be extended to have some sort of event mechanism. Personally I would use an object rather than an array but I guess there are reasons for this?

var object = [];
_.extend(object, Backbone.Events);
 object.on("alert", function(msg)
{
   console.log("Your name is: "+msg);
 });

object.trigger("alert","Sarah");

thanks, there is actually no reason for this, the original code is coded with "{}" too — Gabriel ThaKid, Feb 20 '14 at 16:08

what's the difference between { } and [ ] in javascript

2 Answers2