The development of jQuery plug-ins includes two types:
One is class-level plug-in development, that is, adding new global functions to jQuery, which is equivalent to adding methods to the jQuery class itself. jQuery's global functions are functions that belong to the jQuery namespace. The other is object-level plug-in development, which is to add methods to jQuery objects. The following is a detailed description of the development of the two functions.
1. Class-level plug-in development
The most direct understanding of class-level plug-in development is to add class methods to the jQuery class, which can be understood as adding static methods. A typical example is the $.AJAX() function, which is defined in the jQuery namespace. Plug-in development at the class level can be extended in the following forms:

1.1 Add a new global function

To add a global function, we only need to define it as follows:

jQuery.foo = function() {
alert('This is a test. This is only a test.');
};