How to turn any jQuery plugin into a WordPress one

Part 1: Anatomy of a jQuery Plugin

In this part, we'll analyse what a jQuery plugin is usually made of, where each of those elements should be placed, and how do we usually work with them. Throughout this article, we'll take for example the jQuery FancyBox plugin, (even if there is an existing WordPress adaptation for it already, it's just to have a concrete example).

A) The Javascript Source

jQuery is a javascript library, and plugins are there to help us extend the capabilities of it, so they are written following the same jQuery syntax. Every plugin you'll download is written within a javascript file. That is the core of your plugin, what the developer wrote to allow you to enjoy its functionalities. You then have to include this script in your application:

//Include the plugin script
<script type="text/javascript" src="Path_to/jquery.fancybox.js"></script>

B) The Javascript Snippet

Once you have included the plugin script within your application, most of the time you'll be asked to write a little snippet of code that will make your site or application use the plugin when required. Most of the time, those few lines of code you'll have to write are here to make the plugin work with a particular element of your page, and after a particular event, for example, you say that a FancyBox will appear after a click on a particular link, for example:

//Write the plugin setup
<script type="text/javascript">
jQuery(document).ready(function(){
    //Fancybox
    jQuery("a.fancy").fancybox({
        overlayShow: true,
        overlayOpacity: 0.7
    });
});
</script>

C) Additional Styles

Some plugins sometimes come up with their own stylesheet, modal windows for example. Those styles are required for the plugin to work and therefore need to be included in your application:

//Include the plugin Stylesheet
<link rel="stylesheet" type="text/css" href="Path_to/jquery.fancybox.css" />

D) How to set everything up?

Once you have all your files ready, it's a common good practice to put the styles in the header, and the scripts in the footer, just before the closing </body> tag.  

Part 2: How can we translate this into WordPress?

Now that we understand what the different elements we find in a jQuery plugin are, and where they are supposed to go, let's see how we can do that in WordPress.

How to declare a WordPress plugin?

A) In WordPress, plugins are stored in the /wp-content/plugins directory. So just go in there, and create a directory named after your plugin. In our case, we'll just create a directory called FancyBox. B) In this directory, copy all your jQuery plugin files, (script, styles, images or anything that has to be included with the plugin). C) Then, create a file called init.php. Init.php is the particular file we need to build to allow WordPress to recognize our plugin. Open init.php and copy the following information in it:

/*
Plugin Name: FancyBox //Your plugin name (here we'd write Fancybox)
Plugin URI: http://www.jdmweb.com/resources/fancybox //Url of your choice
Description: Implementation of the FancyBox for jQuery //Brief PLugin Description
Version: 1.0 //Version of your plugin
Author: Jeremy Desvaux //Name of the author
Author URI: http://jdmweb.com/ //Url of your site
License: Creative Commons Attribution-ShareAlike //Licence
 
//Other terms and conditions
 
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
*/

As you can see, in those few lines, we specify a name, a URL, a description and a few other similar piece of information. Those information are being used by WordPress inside the plugin administration interface as you can see on the following picture: From this picture, we see that our 'plugin' has been recognized by WordPress, and contains all the information we wanted. It is time to make it work now. From what we've seen in part one, we need to tell WordPress to put some of our plugin files in the page header, and some in the page footer.

How to specify what goes in the Header ?

What we want to do is to put our plugin stylesheet inside the page header. In html, we do so by adding a link tag in the header. In WordPress, there is a specific method called wp_enqueue_style() (Codex ref here), that allows you to do that. wp_enqueue_style() takes several parameters, mainly the name of your stylesheet and its source for it to work. You can also add dependencies (other styles that need to be included before), and a version number. So In our case, in order to tell our plugin to put its stylesheet inside the header, we would add this inside our init.php file:

//Add the stylesheet into the header
wp_enqueue_style("jquery.fancybox",WP_PLUGIN_URL."/jQuery2Wp_fancybox/jquery.fancybox-1.3.1.css",false,"1.3.1");

Line 3 you can see the name we gave to our stylesheet, line 4 we specify its source, with the constant WP_PLUGIN_URL holding the path to the plugin directory. So if the user decides to move its plugin directory the path won't break. Line 5 false means that this stylesheet has no dependencies, and line 6 1.3.1 is the stylesheet version. That's it for the header, in fact, to recapitulate, instead of adding the stylesheet in our header by ourselves as you would do in a normal application, you just ask WordPress to do it for you.

How to specify what goes in the Footer ?

In a very similar fashion, to add our scripts inside the WordPress footer, there's a function we can use as well. It is called wp_enqueue_script(), (Codex ref here). wp_enqueue_script() accepts parameters that are very similar to wp_enqueue_style, meaning a script name, path, dependencies, en version. The last parameter is a boolean, and specifies whether you want to enqueue the script in your header (if set to 0), or in your footer (if set to 1), so in our case, because we want to enqueue them in the footer, we'll set the boolean to 1. Let's then use wp_enqueue_script() to add our scripts:

//Add the scripts in the footer
wp_enqueue_script("jquery");
wp_enqueue_script(
"jquery.fancybox", WP_PLUGIN_URL."/jQuery2Wp_fancybox/jquery.fancybox.js",
array("jquery"), "1.3.1",1);	
wp_enqueue_script(
"jquery.fancyboxsetup", WP_PLUGIN_URL."/jQuery2Wp_fancybox/fancybox-setup.js",
array("jquery","jquery.fancybox"), "",1);

Line 3 and 6, you can see wp_enqueue_script in action. We add our plugin scripts by specifying their name, path, dependencies, version and we place them in the footer with the 1 in the end. As you can see, the FancyBox script has one dependency, which is jQuery, and the FancyBox setup has 2, (jQuery and the FancyBox).

Time To Test

Your plugin is now ready to work. If you go back to the administration interface, in the plugin section, and activate the plugin, WordPress will add your files in the correct places, and your plugin will start working!

How to use the plugin on specific pages only?

Now that your plugin is activated, from the code we wrote in our init.php file, WordPress will automatically add our files in the header and the footer of every page of our application. This can be right if you effectively need to use this plugin on nearly every page of your site, but if it is not the case, it's more of a waste of resource, and a bigger page load time for nothing. I'm going to show you a little technique if you'd like to include the plugin only on certain pages. It's very simple The trick is to gather the little snippets of code we just wrote, and to put them into one function, that we're going to call FancyBox_wp_setup():

//Group the code inside a function
function fancybox_wp_setup(){
    wp_enqueue_style(
    "jquery.fancybox", WP_PLUGIN_URL."/jQuery2Wp_fancybox/jquery.fancybox-1.3.1.css",
    false, "1.3.1");
    wp_enqueue_script("jquery");
    wp_enqueue_script(
    "jquery.fancybox", WP_PLUGIN_URL."/jQuery2Wp_fancybox/jquery.fancybox.js",
    array("jquery"), "1.3.1",1);	
    wp_enqueue_script(
    "jquery.fancyboxsetup", WP_PLUGIN_URL."/jQuery2Wp_fancybox/fancybox-setup.js",
    array("jquery","jquery.fancybox"), "",1);
}

This has actually 2 different effects. It prevents WordPress from including your pages on every page, which is something we wanted, and it also gives you access to the function FancyBox_wp_setup(), that you can call on every page template you want to use the plugin on.

Conclusion

When you find the perfect jQuery plugin for your design, integrating it properly for a WordPress use is just a few lines of code away! I hope that next time you'll find a plugin you wish to use, you'll remember this article and you'll turn your plugin into a WordPress one in 5 minutes.