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

This question already has answers here: Closed 11 years ago.

Possible Duplicate:

What does this “(function(){});”, a fu开发者_开发百科nction inside brackets, mean in javascript ?

(function(){
    ---this code at here ----
})();

What does (function(){})(); mean? Please explain it to me.

---

It makes an anonymous function and executes it. You use it to prevent variables from poluting the global scope.

(function(){
  var test = "Hello";
})();

alert(test); //test will be undefined here

---

The function is immediately executed after parsing it.

---

Well, you use a function expression as a closure which gets executed immediately and 'this code at here' will not pollute global namespace.