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Returning functions

Functions are objects, so they can be passed around like callbacks for example and also returned by other functions.

You call a function that does some complicated setup and as a results returns a new function. You assign the result to a new function and use it afterwards.

function setup() {
    alert(1);
    return function() {
        alert(2);
    };
}
var my = setup(); // alerts 1
my(); // alerts 2

Your setup function can store some private data in a closure and use that data somehow.

Here setup() creates a counter function, which gives a next ID for example. But the count variable is not exposed.

function setup() {
    var count = 0;
    return function() {
        return ++count;
    };
}
var next = setup();
next(); // 1
next(); // 2

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This entry was posted on Tuesday, September 15th, 2009 and is filed under Functions. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.

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