Why won't this JavaScript function fire?

Question

I wrote a small hash change object, it will alert the url hash whenever it changes:

(function() {
 function hashChange() {
 this.previousHash;
 this.initialize();
 }
 hashChange.prototype.initialize = function() {
 this.setInterval = window.setInterval(this.checkHashChange, 0);
 }
 hasChange.prototype.uponHashChange = function(hash) {
 alert('I executed!');
 var hashValue = hash.split('#')[1];
 alert(hashValue);
 }
 hashChange.prototype.checkHashChange = function() {
 var hash = window.location.hash;
 if(hash && hash !== this.previousHash) {
 this.previousHash = hash;
 this.uponHashChange(hash); // <---- doesn't execute
 }
 }
 var hashChange = new hashChange();
})();

But this:

this.uponHashChange(hash);

Never gets executed. Why?

• Matt Greer: checkHashChange will run in the context of the global object. You need something like Function.bind.

Answer 1

this.setInterval = window.setInterval(this.checkHashChange, 0);

This line is not going to do exactly what you mean. this.checkHashChange will lose its binding to its current this (which would be a hashChange instance), and will instead be invoked in the context of the window object.

You need to bind it explicitly to the correct context object:

var self = this;
this.setInterval = window.setInterval(function() { self.checkHashChange() }, 0);

Matt Greer has suggested Function.bind, which would make it more concise and likely more readable:

this.setInterval = window.setInterval(checkHashChange.bind(this), 0);

Unfortunately, Function.bind is not yet widely supported across browsers.

• user967451: ok but none of this changes the issue with that non executing method: TypeError: this.uponHashChange is not a function, same error even if I store this inside a variable and reference it that way: TypeError: self.uponHashChange is not a function
• lanzz: Please post your updated code, I have no way to know how you have altered your code, considering I haven't advised you to change your uponHashChange invocation at all.
• user967451: wait never mind, it works now. The bind method wasn't working but the 1st suggestion works. The bind method was giving the uponHashChange error.