Question

175

What is a practical use for a closure in JavaScript?

rated 0 times [ 180] [ 5] / answers: 1 / hits: 142722 / 14 Years ago, wed, april 28, 2010, 12:00:00

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();

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destiniemartinac

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2 Years ago

answered 14 Years ago blaisep · Accepted Answer

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.