jQuery UI Design Pattern Question

Question

I'm reading through the jQuery UI source code (ui-dialog specifically), I see this pattern repeated many times:

    var self = this,
        options = self.options,
        uiDialog = self.uiDialog;

What's the reasoning behind this pattern of, var self = this, something, something else

Answer 1

it's just caching variables && obect propertys. This in general is considered as very good practice since object lookups come with a cost.

window.href

takes much more time than

var myhref = window.href;
myhref;

Of course you need to make the expensive call once, but all further calls to the cached variable are much much faster.

Another reason for using this pattern is to cache DOM node references for pretty much the same reasons. Accessing the DOM is one of the most expensive things you can do in Javascript (in a browser). So by caching references you just boost your code.