could you explain the function in javascript?

Question

Possible Duplicate:
What does this mean? (function (x,y)){…}){a,b); in JavaScript

(function(){
    var foo = 'Hello world';
})();

i don't know what's use of it? and what's meaning of it/?

Answer 1

On its own it does nothing except declare a variable that isn't used - it should invoke some other functions to do something useful.

That said, what you have is an immediately invoked function expression, i.e. an anonymous function:

function() { ... }

which is invoked with no parameters:

(f....)();

The rationale is two fold:

• it allows the function to be defined and called without giving it a name in the global name space
• any variables defined within the function are also held within that scope, and don't pollute the global name space.

Answer 2

It's an anonymous function that executes immediately.

The idea is to create a private scope. Often one would return a closure from the anonymous function that retains access to variables created in that scope.

For example

var greet = (function () {
    var foo = 'Hello world';
    return function () {
        alert(foo);
    }
}());

greet();

Answer 3

This calls an anonymous function immediately.

Have a look here: What does this “(function(){});”, a function inside brackets, mean in javascript ?