Question

I’m trying my hardest to wrap my head around JavaScript closures.

I get that by returning an inner function, it will have access to any variable defined in its immediate parent.

Where would this be useful to me? Perhaps I haven’t quite got my head around it yet. Most of the examples I have seen online don’t provide any real world code, just vague examples.

Can someone show me a real world use of a closure?

Is this one, for example?

var warnUser = function (msg) {
    var calledCount = 0;
    return function() {
       calledCount++;
       alert(msg + '\nYou have been warned ' + calledCount + ' times.');
    };
};

var warnForTamper = warnUser('You can not tamper with our HTML.');
warnForTamper();
warnForTamper();

Answer 1

I’ve used closures to do things like:

a = (function () {
    var privatefunction = function () {
        alert('hello');
    }

    return {
        publicfunction : function () {
            privatefunction();
        }
    }
})();

As you can see there, a is now an object, with a method publicfunction ( a.publicfunction() ) which calls privatefunction, which only exists inside the closure. You can not call privatefunction directly (i.e. a.privatefunction() ), just publicfunction().

It’s a minimal example, but maybe you can see uses to it? We used this to enforce public/private methods.