Question

I saw this syntax many times but I couldn’t find a way to google it properly, I hope I can get some help here:

  <script>
    (function(){
      //code goes here
    })();
  </script>

Why is the function keyword wrapped in the parenthesis? What does it do and what is this called?

Answer 1

In js, the syntax:

function() { //code }

defines an anonymous function. You can store this into a variable and call it:

var a = function() { //code };
a();

or if you don’t want to bother assigning it you can do it in one step.

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

the parenthesis are necessary because:

function() { //code }();

is not proper syntax.

This syntax is useful in certain situations to help memory management as well as change variable names. For example in javascript you have a jQuery object, but most people refer to it as $. But sometimes $ is used as some other variable instead of the jQuery object. To fix this, you can wrap your code in:

(function($) { // code that uses $ })(jQuery);

That way you can use the dollar sign and not have to worry whether or not it actually points to the jQuery object or not.