All of the answers were good, but I think the simplest answer has been skimmed over:
var something = (function(){
//do stuff
return stuff;
})()
After this code executes, something becomes stuff. The function that returned stuff is executed before something is assigned.
var something = function(){
//do stuff
return stuff;
};
After this code executes, something is a function which returns stuff. The function that returns stuff was never executed.
