jQuery - Plugins

A plug-in is piece of code written in a standard JavaScript file. These files provide useful jQuery methods which can be used along with jQuery library methods.
There are plenty of jQuery plug-in available which you can download from repository link at https://jquery.com/plugins.
To make a plug-in's methods available to us, we include plug-in file very similar to jQuery library file in the <head> of the document.
We must ensure that it appears after the main jQuery source file, and before our custom JavaScript code.
Following example shows how to include jquery.plug-in.js plugin −
<html>
   <head>
      <title>The jQuery Example</title>
		
      <script type = "text/javascript" 
         src = "https://ajax.googleapis.com/ajax/libs/jquery/2.1.3/jquery.min.js">
      </script>

      <script src = "jquery.plug-in.js" type = "text/javascript"></script>
      <script src = "custom.js" type = "text/javascript"></script>
      
      <script type = "text/javascript" language = "javascript">
         $(document).ready(function() {
            .......your custom code.....
         });
      </script>
   </head>
	
   <body>
      .............................
   </body>
</html>
This is very simple to write your own plug-in. Following is the syntax to create a a method −
jQuery.fn.methodName = methodDefinition;

Here methodNameM is the name of new method  and methodDefinition is actual method definition.
The guideline recommended by the jQuery team is as follows −
Any methods or functions you attach must have a semicolon (;) at the end.
Any methods or functions you attach must have a semicolon (;) at the end.
Your method must return the jQuery object, unless explicity noted otherwise.
Your method must return the jQuery object, unless explicity noted otherwise.
You should use this.each to iterate over the current set of matched elements - it produces clean and compatible code that way.
You should use this.each to iterate over the current set of matched elements - it produces clean and compatible code that way.
Prefix the filename with jquery, follow that with the name of the plugin and conclude with .js.
Prefix the filename with jquery, follow that with the name of the plugin and conclude with .js.
Always attach the plugin to jQuery directly instead of $, so users can use a custom alias via noConflict() method.
Always attach the plugin to jQuery directly instead of $, so users can use a custom alias via noConflict() method.
For example, if we write a plugin that we want to name debug, our JavaScript filename for this plugin is −
jquery.debug.js

The use of the jquery. prefix eliminates any possible name collisions with files intended for use with other libraries.
Following is a small plug-in to have warning method for debugging purpose. Keep this code in jquery.debug.js file −
jQuery.fn.warning = function() {
   return this.each(function() {
      alert('Tag Name:"' + $(this).prop("tagName") + '".');
   });
};
Here is the example showing usage of warning() method. Assuming we put jquery.debug.js file in same directory of html page.
<html>
   <head>
      <title>The jQuery Example</title>
		
      <script type = "text/javascript" 
         src = "https://ajax.googleapis.com/ajax/libs/jquery/2.1.3/jquery.min.js">
      </script>
		
      <script src = "jquery.debug.js" type = "text/javascript">
      </script>

      <script type = "text/javascript" language = "javascript">
         $(document).ready(function() {
            $("div").warning();
            $("p").warning();
         });
      </script>	
   </head>
	
   <body>
      <p>This is paragraph</p>
      <div>This is division</div>
   </body>
</html>
This would alert you with following result −
This is paragraph
This is division


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