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:

// do something

I first thought this is just for local scoping, i.e. creating local variables for the code block without polluting global namespace. But I've seen instances without any local variables at all too.

What am I missing here?

Answer 1

It's about scope for functions, too - everything declared within the code block is scoped to that anonymous function only. Things are normally made public by the framework

(function($) {

  var localVarOnly = "local";

  $.fn.myCoolFunction = function() { // in the case of jquery, make this publicly available
    otherCoolFunction(); //alerts hi
    alert(localVarOnly); // alerts local
  };

  function otherCoolFunction() { // scoped to this anonymous function only
    alert('hi');
  };

})(jQuery);

otherCoolFunction(); // undefined
alert(localVarOnly); // undefined