JavaScript this keyword, that, and callbacks

ThisThatAndCallbacks.js

this.foo = 'bar';
console.log(this.foo); // prints 'bar'
var that = this; // save a reference
$('#myButton').click(function(event) {
  console.log(this.foo); // prints 'undefined' since it's not the same 'this'
  console.log(that.foo); // prints 'bar'
});

See CoffeeScript: JavaScript that’s easy on the eyes for more information.