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.