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

Answer 1

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

Answer 2

The function is immediately executed after parsing it.

Answer 3

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