Glossary: Closure

A "closure" is a function that has data intrinsically bound to it, for instance by virtue of where it's defined. This is a closure:

var a;
a = 5;
function myFunction()
{
    // ...
}

"myFunction" is a closure: The 'a' variable is bound to it, because 'a' is in scope where 'myFunction' is defined. There's also a closure here:

var a;
 
a = ['a', 'b', 'c'];
a.each(function(v) {
    alert(v);
});

The anonymous function used with the each method is a closure.

More on closures:

• http://en.wikipedia.org/wiki/Closure_(computer_science)
• http://blog.niftysnippets.org/2008/02/closures-are-not-complicated.html