jQuery (function(a){...})(jQuery);

Question

I get a *.js file code similar like:

(function(a){ 

   a("#div_element").removeClass("show message");
 
   ....

})(jQuery); 

I'm trying to understand:

1. What is (function(a){...})(jQuery); ?

2. How to use it?

3. What is a here? Because I seen normal code looks like:

   $("#div_element").removeClass("show message");

Answer 1

function( a ){ /* … */ } is an anonymous function that is directly called with jQuery as parameter. So a inside the anonymous function is the same as jQuery

From jQuery website

Example: Reverts the $ alias and then creates and executes a function to provide the $ as a jQuery alias inside the functions scope. Inside the function the original $ object is not available. This works well for most plugins that don't rely on any other library.

jQuery.noConflict();
(function($) { 
  $(function() {
    // more code using $ as alias to jQuery
  });
})(jQuery);
// other code using $ as an alias to the other library

read this post also:

What does (function( $ ){...})( jQuery ); do/mean?

Answer 2

Maybe it's easier to understand the mechanism by thinking of it this way:

(function( blah ) {
    blah("hello");
}) ( alert );

Note how blah becomes a proxy for alert. This is just a fancy way of not polluting the global namespace (a lot of libraries use the $ as a global variable).