Question

I have a javascript class object that I want to use multiple times on the same page, and it requires a setTimeout function to work as it keeps ticking over in the background. However, as you can see in this fiddle, on the timeout call, its only referencing the newest instance of the object. Does anyone know how I can sort it? Preferably, I would like to see how it is done not in jQuery, I like to understand exactly how it does it.

http://jsfiddle.net/cgoddard/yQDLe/20/

Answer 1

When you write this.doDelayed inside a doubly nested function, the this keyword doesn’t refer to your test object. Instead, it refers to whatever object the currently executing function was called for, which is probably window.

To overcome this, you have to save your this in the very beginning of the test function, say like this: var $this = this;
Then you can refer to that very object using $this.

Besides this, when you write simply x = something, the symbol x is treated like a property on the window object (also known as “global variable”). Therefore, both your doDelayed and construct functions end up on the window object. Consequently, when you do this second time, they both get overwritten. This is why you get same results twice.
Instead, you should write $this.doDelayed = function() ... (where $this is your saved value of this from above), and do similarly for construct.