javascript self executing syntax

Question

Did anyone know the code which define like this:

!function(window, undefined) {
    // do something
} (window)

By searching in google, I can understand the syntax like:

function(window, undefined) {
    // do something
} (window)

But I don't figure out any article about the syntax have "!" operator.

score 3 · Accepted Answer · answered Jun 03 '13 at 06:57

3

The ! operator is there so the function is parsed as an expression, rather than a declaration. Since a declaration cannot be invoked, your second example is a syntax error.

A more commonly seen form is to enclose the function in parentheses:

(function(window,undefined) {
    // do something
}(window));

That has exactly the same effect, as does the use of any unary operator.

answered Jun 03 '13 at 06:57

James Allardice

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I think you mean (function(window,undefined) { ... })(window); – francisco.preller Jun 03 '13 at 07:00
I just came by this thread and was curious. By expression you mean like i.e an if statement? `if (function()) {}`? – CaptainCarl Jun 03 '13 at 07:00
the exclamation mark transform the definition into an expression so that the parenthesis can call it right after because it has higher priority, `!function(){}()` is an evil version of `(function(){})()` – Frederik.L Jun 03 '13 at 07:04

score 0 · Answer 2 · answered Jun 03 '13 at 06:58

0

It might be like this.

!(function(window, undefined){ /* some code */ })(window);
(function(window, undefined){ /* some code */ })(window);

answered Jun 03 '13 at 06:58

Edward

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javascript self executing syntax

2 Answers2