Lay the groundwork: about $.fn and $.fn.extend.

While JavaScript does not have a class concept, it is understandable that jquery is equivalent to a class in JavaScript, while $.extend adds a static method to the jquery class.

$.extend ({   function(A, b) {return (A +b);}    ; function (A, B) {return (A-b);};}) // you can directly use the newly added jquery method Console.log ($.add (3,4));      // 7

But what about $.fn.extend?

Let us first understand what is Fn:$.fn equivalent to Jquery.prototype, then $.fn.prototype is equivalent to prototype to expand, add a member function for jquery. To refer to this function, you must create a new jquery object. This method of adding member functions to jquery is often used in the development of plug-ins, as in the following example:

$.fn.extend ({    function() {      $ (this). Style.display = "None" ;     };}); $ ("#hide_this"). hidden ();  // $ ("") is a jquery object that calls its hidden method to make the element hidden. 

Lay the groundwork: about $.fn and $.fn.extend.