javascript function vs. ( function() { ... } ());

Question

I have often see expressions such as:

(function () {
    var x = 1;
    ...
}());

How do I interpret it? syntactically, this alone is a anonymous function definition.

function() {
...
}

what the () after that? and why put it in the enclosing ()?

Thanks

Answer 1

Exactly the same, except that it is being invoked immediately after being converted into a function expression.

// v-----first set of parentheses makes the function an expression
   (function () {
       var x = 1;
       ...
   }());
//  ^-----this set is used to invoke the function

Same as if you did:

   var myfunc = function () {
       var x = 1;
       ...
   };
   myfunc();

or (similar) this:

   var returnValue = function () {
       var x = 1;
       ...
   }();

Get rid of the names, move the parentheses around, and you can see they're not that different.