What is this format of function called?

Question

function animator(shapes, $timeout) {
    (function tick() {
        var i;
        var now = new Date().getTime();
        var maxX      = 600;
        var maxY      = 600;
        var now = new Date().getTime();

        $timeout(tick, 30);
    })(); // What is this for?
}

Here I don't understand the functionality. I am new to this kind of script. Inside of the main function is like ()(). What is this for?

I think it's called a self invoking function...A function that is defined and immediately executed. — Lix, Aug 13 '15 at 11:57
Possible duplicate: [iife - What is the (function () {})() construct in javascript?](http://stackoverflow.com/q/8228281/1168892) — Dominik Schreiber, Aug 13 '15 at 11:58

score 7 · Answer 1 · answered Aug 13 '15 at 11:59

This is an IIFE, Immediately-invoked function expression.

Why use an IIFE?

Why?: An IIFE removes variables from the global scope. This helps prevent variables and function declarations from living longer than expected in the global scope, which also helps avoid variable collisions.

Why?: When your code is minified and bundled into a single file for deployment to a production server, you could have collisions of variables and many global variables. An IIFE protects you against both of these by providing variable scope for each file.

score 3 · Answer 2 · edited Apr 09 '17 at 06:07

3

I don't know if it has a separate name, it's just immediately executed.

Instead of function a(){..}; a() you can do (function(){..})()

Useful for scoping the vars inside, while placing/executing it right where you want it, also you don't have to invent a name for it.

edited Apr 09 '17 at 06:07

Rodia

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answered Aug 13 '15 at 11:59

birdspider

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score 2 · Answer 3 · answered Aug 13 '15 at 12:01

2

(function(){console.log('test')})() will call function immediately. So if you will write this statement then it will be called immediately and prints test on console.

answered Aug 13 '15 at 12:01

Juned Lanja

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score 1 · Accepted Answer · edited Jun 20 '20 at 09:12

1

This is a self-invoking function as @lix pointed out.

Function expressions can be made "self-invoking".

A self-invoking expression is invoked (started) automatically, without being called.

Function expressions will execute automatically if the expression is followed by ().

edited Jun 20 '20 at 09:12

Community

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answered Aug 13 '15 at 12:01

Shambhavi

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What is this format of function called?

4 Answers4