JS function definition : meaning of the last parentheses

Question

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What is the purpose of a self executing function in javascript?
What does this mean? (function (x,y)){…}){a,b); in JavaScript

I see sometimes functions defined like these examples :

(function() {
    ....     
})();

(function(param) {
    ....     
})(JQuery);

(function(chat, Friend) {
    ....     
})(chat, chat.module("friend");

After some web researches, I didn't find any information about the meaning of the last parentheses information.

Is there someone to explain how to use it? Or simply point a web link explaining the meaning?

http://benalman.com/news/2010/11/immediately-invoked-function-expression/ — SLaks, Dec 31 '12 at 15:56
Which brackets (parenthesis?) do you mean exactly? Some of these aren't even valid syntax. — Matti Virkkunen, Dec 31 '12 at 15:57

score 2 · Answer 1 · answered Dec 31 '12 at 16:00

Suppose we had:

function add1 (x) {
    return x+1;
}

Then we might call add1(5) to get the value 6.

But with the brackets, rather than calling add1(5), we can replace it with (function (x) {return x+1;})(5). Basically this creates a function, and applies it to the value 5 immediately, whereas when we call add1(5), we are using a named/defined function.

Nope · Accepted Answer · 2012-12-31T16:06:11.663

2

meaning of the last brakets

(function() {
    ....     
})();

The () in the end causes the code inside the function to be executed immediately.

(function(param) {
    ....     
})(JQuery);

The (JQuery) in the end causes the code inside the function to be executed immediately, passing JQuery as a parameter to it.

(function(chat, Friend) {
    ....     
})(chat, chat.module("friend"));

The (chat, chat.module("friend")) in the end causes the code inside the function to be executed immediately, passing chat and chat.module("friend") as parameters to it.

edited Dec 31 '12 at 16:06

answered Dec 31 '12 at 16:01

Nope

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The parentheses are unmatched in code examples #1 and #2. You should fix that for the asker. – John Dvorak Dec 31 '12 at 16:04
@JanDvorak: Thanks. I didn't notice that, I assume it is a copy-paste error. I fixed them now. – Nope Dec 31 '12 at 16:07

score 0 · Answer 3 · edited May 23 '17 at 12:15

0

Check out this question: What is this practice called in JavaScript?

Basically, the function will execute with the parameters you pass it. In this example, param will have the value of jQuery:

(function(param) {
    ....     
})(JQuery);

edited May 23 '17 at 12:15

Community

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answered Dec 31 '12 at 15:59

KaeruCT

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It should be an error. The line `})(JQuery);` would be valid, as would `}(JQuery));`, but not `})(JQuery));` unless your starting function statement looks like `((function ($) {` for no reason. – Norguard Dec 31 '12 at 16:02

JS function definition : meaning of the last parentheses

3 Answers3

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