Bound methods in Javascript
The popular way to create a class in Javascript is to define a function and add methods to its prototype. For example, let’s create a class Node that has a method hide(). var Node = function(id) { this.element = document.getElementById(id); }; Node.prototype.hide = function() { this.style.display = "none"; }; If you had a header, say Heading, then this piece of code will hide the element. var node = new Node("header"); node.hide(); If I wanted to hide the element a second later, I am tempted to use: var node = new Node("header"); setTimeout(node.hide, 1000); … except that it won’t work. setTimeout has no idea that the function node.hide has anything to do with the object node. It just runs the function. When node.hide() is called by setTimeout, the this object isn’t set to node, it’s set to window. node.hide() ends up trying to hide window, not node. ...