What does ||{} mean in javascript?

Question

I'm working on a project using Easel JS. Opened up the Easel file and the very first line of code confused me:

this.createjs = this.createjs||{};

I know that createjs is invoked when you're setting up your canvas or, for example, creating a bitmap to add to the canvas. But I don't understand the syntax of this line - assign this.createjs or (what I guess is) a blank object to this.createjs?

if this.createjs object does not exist initialize this.createjs as an object… is what it means.. — Sudhir Bastakoti, Mar 31 '15 at 10:21
It means: If this.createjs isn't undefined then use this.createjs otherwise use an empty object. — Bhojendra Rauniyar, Mar 31 '15 at 10:22
if this.createjs is falsy (undefined, false, etc) it will be replaced by empty object. — biera, Mar 31 '15 at 10:22
You can consider this as setting a default value for `this.createjs`. The default value is an empty object `{}` if an existing value does not exist. — Lix, Mar 31 '15 at 10:24

score 6 · Accepted Answer · answered Mar 31 '15 at 10:22

this.createjs = this.createjs||{};

If this.createjs is not available/ any falsy value then you are assigning {} empty object to this.createjs.

It's more like,

var a, 
    b;

b = a || 5;

Since a is not having any value currently, 5 will be assigned to b.

score 2 · Answer 2 · answered Mar 31 '15 at 10:22

2

Correct. This ensures that if this.createjs doesn't already exist, an empty object is assigned to it. The || is an or operator - if this.createjs on the left-hand-side evaluates to falsy, it will assign the right-hand-side instead.

answered Mar 31 '15 at 10:22

Andrew Ferrier

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score 2 · Answer 3 · answered Mar 31 '15 at 10:23

2

this.createjs = this.createjs||{};

If this.createjs is falsy, this.createjs will be a new empty object

You could have replace it by

if (!this.createjs){
     this.createjs = {};
}

answered Mar 31 '15 at 10:23

Deblaton Jean-Philippe

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score 1 · Answer 4 · answered Mar 31 '15 at 10:22

1

|| means or. In that context means this.createjs equals if exists/not null/defined this.createjs other way {}

answered Mar 31 '15 at 10:22

naoxink

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What does ||{} mean in javascript?

4 Answers4