I'm a web developer, but lots of folks are looking for slightly more advanced skills and understanding closures seems to be at the forefront of this.
I get the whole "execution context creating a reference to a variable that doesnt ever get destroyed" thing, but really, is this some sort of private or static variable implementation in JavaScript?
They can be good for lots of things, for example, visibility (like private members in traditional OO).
var count = function(num) {
return function(add) {
add = add || 1;
num += add;
return num;
}
}
My count() can be seeded with a number. When I assign a variable to the return, I can call it with an optional number to add to the internal num (an argument originally, but still part of the scope of the returned function).
This is a pretty good overview.
A closure is a code block with bound variables - it "catches" its variables from their outer context - but it is independent from that same context.
A practical use in javascript is when defining events or callbacks - you declare a closure to be executed on the click of a button, for instance, but this closure can reference variables declared on the caller scope.
jQuery uses closures a lot - btw this is a good link for understanding closures for jQuery: A Graphical Explanation Of Javascript Closures In A jQuery Context.
Hope it helps.
There are many JS books available, but you really should grab a copy of David Flanagan's JavaScript: The Definitive Guide if you really want to learn this (still the best JS reference IMHO). Read the chapter on closures and you'll get a lot more in-depth knowledge than anyone can give you in a reply here.
