JavaScript - How do I learn about “closures” usage?

Question

From Wikipedia, the free encyclopedia: Closure (computer science)

In computer science, a closure is a function that is evaluated in an

Answer 1

(using an example from jQuery)

function SetClassOnHover(className){
  $("td").hover(
    function () {
      $(this).addClass(className);
    },
    function () {
      $(this).removeClass(className);
    }
  );
}

The closure comes into play when the variable className is used inside the scope of each function. When SetClassOnHover exits, both functions must retain a handle on className in order to access its value when the functions are called. That's what the closure enables.

Answer 2

A practical example of closures is when they are used to create "Private" variables, like

function incrementer(){
    var i=0;
    this.increment=function(){
        i++;
    }
    this.get=function(){
        return i;
    }
}

The only way to access i is to use the method get, and the only way to change it is to use the method increment. In classes, you can do this to emulate private variables.

Answer 3

Searching for "javascript closures" gave plenty of encouraging-looking links. The top three were these two (the third link was a reformatted version of the second):

• Javascript closures
• JavaScript closures for dummies

If these didn't help you, please explain why so we're in a better position to actually help. If you didn't search before asking the question, well - please do so next time :)