Sometimes it’s difficult to find an easy answer to common coding questions. Because Google ignores most punctuation, even the most exact queries fail to produce relevant results. Questions about the nature and value of this in Javascript present a particularly thorny problem, since “this” is about as common a word as you can find.

A common point of confusion in Javascript is that the value of this depends entirely on a function’s context, and can even be overridden depending on how a function is invoked. Hopefully this post will save time for new Javascript devs trolling through Google’s depths:

In anonymous functions, the value of this refers to the anonymous function itself, and not the calling scope. However, the nature of closures allows the anonymous function to still refer to the calling object.

The above rule is demonstrated with the following nodejs code:

1
2
3
4

var that = this;
that.foo = 'bar';
process.nextTick(function() {
  console.log("this " + this.foo + " and that " + that.foo) });