Question

What exactly does this do? I know that it gets wrapped around jquery plugins, but have no real understanding of what it does.

(function ($, undefined) {

// Plugin goes here

})(jQuery);

Answer 1

()() is a way to run a piece of code in javascript. The first pair of parentesis is the code part and the second is for execute order and you can pass variables like calling a function.

Within first parentesis you define your function, which takes two arguments and you execute it with a parameter jQuery which is core jQuery object. To do so, you are passing jQuery object to your function as a variable and name it $. Because your function is defined in that scope your code doesn’t conflict with another $ variable on global scope or scope that contains your code.

As you can see there is another variable: undefined but no parameter for it. By not passing a second parameter second variable will be undefined and because it’s name is undefined you can use it in your code freely. For more info about undefined you can look here

I hope this is clear enough.