Why do many javascript libraries begin with “(function () {”?

Question

Why do many javascript libraries look like this:

(function () { 
    /* code goes here */ 
})();

It appears to define an unnamed function whic

Answer 1

If forces scope declaration. By putting it in a function you are making sure that the variables you create and call aren't being re-declared or you aren't accidentally calling variables which are declared elsewhere.

so.....

var variable = 5; // this is accessible to everything in the page where:

function ()
{
   var variable = 7 // this is only available to code inside the function.
}

Here is a link to Douglas Crockford's site talking about scope in Javascript:

http://javascript.crockford.com/code.html

to follow up on the comment below:

JavaScript's scope is a little "broken":

function ()
{
   var x = 3;  // accessible in the entire function.
   //for scope reasons, it's better to put var y = 8 here.....
   if(x != 4)
   {
       var y = 8; //still accessible in the entire function. 
                  //In other languages this wouldn't be accessible outside 
                  //of the if statement, but in JavaScript it is.  

   }

}