Newbie Javascript question

The problem is right there in the error message: You are calling

this.Update(elapsedMS);

in your this.Tick function, but you have not defined an Update function anywhere.

Oops. I realized that I only posted part of the code I have. Here is more relevant code:

//create singleton class
var sim = new function()
{
...
this.Run = function()
	{
		this.tickIntervalId = setInterval(this.Tick, 1000/60); //Update at 60 fps
	};
...

this.Update = function (elapsedMS) {
		
	  for (var i = 0; i < nodeArr.length; i++) {
		nodeArr.Update();
	  }
	};
...
this.Tick = function () 
	{
		var currTime = Date.now();
		var elapsedMS = currTime - this.lastUpdateTime;

		this.Update(elapsedMS);
		this.Render();

		this.lastUpdateTime = currTime;
	};
};

sim.Run();

In JavaScript functions don't really have a "context" associated statically with them, it is evaluated dynamically .. setTimeout and setInterval basically "reset" the context and your call to "this.Tick" doesn't know what "this" is.

Change

If you are running on chrome, you can simply use the bind function,

this.tickIntervalId = setInterval(this.Tick.bind(this), 1000/60); //Update at 60 fps

or if you are using the popular underscore utility

this.tickIntervalId = setInterval(_.bind(this.Tick,this), 1000/60); //Update at 60 fps

The problem is that your Tick function gets called in a global context. Which means that, the 'this' pointer is the global 'this' which is not what you need. Hence you need to bind the 'this' context so that when the Tick function gets called from a global context, the original 'this' pointer is still saved.