Why would one write global code inside a function definition-call pair?

Question

I see examples where JavaScript code including jQuery and jslint use the notation below:

(function(){
  // do something
})();

instead of:

Answer 1

That syntax is to create local scope, as others have commented, but also to make the function self-executing. Note that simply creating local scope could also be accomplished like this:

var foo = function(){
   // local code
};
foo();

But if that's all you're doing, and foo has no other utility beyond calling it one time, then the anonymous, self-executing syntax simply saves you the extra var declaration:

(function(){
   // local code
})();

In frameworks that use OOP patterns, this is also the syntax used to create singletons since the function can only run once and can never be called again by external code.