What does (function () { })();mean? [duplicate]

Question

This question already has answers here:

Closed 13 years ago.

Possible Duplicate:
What is the purpose of a self executing function in javascript?

What meens in JS write a code like this:

(function (window) { })(window);

or this:

(function () { })();

• gdoron: It's a duplicate so I voted to close, though I think the answers there aren't as good as the answers here. specially not this wrong +17 answer
• Franz Holzinger: If someone looks for PHP 7, where this has been introduced. stackoverflow.com/questions/3568410/…

Answer 1

It creates a closure, a private scope hiding the variables from the global object

// Somewhere...
var x = 2;
...
...
// Your code
var x = "foo" // you override the x defined before.
alert(x); // "foo"

But when you use a closure:

var x = 2;
// Doesn't change the global x
(function (){ var x = "foo";})();
alert(x); // 2

Regarding to the syntax, it's just a self executed function, you declare it and then execute it.

• Rodrigo Reis: TY! And when I pass a variable? Like this: (function (window) { })(window);
• gdoron: @RigoReis. They become variables in the function. it's used for minifing code, nothing "real"
• Rodrigo Reis: TY'll folks help me so much, special thanks to @gdoron
• gdoron: @RigoReis. No problem. Good luck in your new js way.

Answer 2

It's a self invoking anonymous function or a function expression. It prevents you from creating variables in the global scope. It also calls the function right away.

function someFunc() {
 // creates a global variable
}
var someFunc = function () {
 // creates a global variable
}
(function(){
 // creates an anonymous function and 
 // runs it without assigning it to a global variable
})();

Answer 3

It's called a closure. It helps control the scope of variables since Javascript hoists variables to the top of their scope. They're also anonymous functions which execute or initialize immediately.