Plugin and theme authors use jQuery for their special effects, but there seems to be some confusion about the proper way to include JavaScript files in WordPress. If you’d like to use jQuery effects on your pages or in your theme, or if you want to include any javascript plugin or personal script, read on to see how to do it properly with WordPress sites.
Queue Up Your Scripts with Actions
Since jQuery itself is already included in the core of WordPress, how should we include a javascript file that we’ve created or even one of the popular jQuery plugins that rely on jQuery? WordPress helps us in this endeavor with a function called ‘wp_enqueue_script()‘ and two actions that are used to call this special function.
The actions are used for either the user side or the admin side, depending on the purpose of your javascript. Use the ‘wp_enqueue_scripts‘ action to call wp_enqueue_script() for use in your themes. If the script functionality is needed on the admin side, use ‘admin_enqueue_scripts‘ action instead.
The format of the wp_enqueue_script() function call is as follows:
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wp_enqueue_script(‘$handle’, ‘$src’, ‘$deps’, ‘$ver’, ‘$in_footer’);
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where $handle is the name of the script as a lowercase string, $src is the URL to the script, $deps is an array of scripts that the script you’re calling depends on or the scripts that must be loaded first for your script to work, $ver is the script’s version number in string format, and $in_footer is a boolean value to indicate whether the script should be loaded in the <head> or at the end of the <body> in the footer.
The $handle string is the only required parameter, so the other four parameters are optional. The $src, $ver, and $in_footer parameters default values are ‘false’, and $deps defaults to an empty array.
It seems that $src would need to be a required option, but WordPress already knows about several scripts and where to find them. Consult the list of default scripts included with WordPress to pick up their handles.
For example, to queue the jQuery Color plugin, we’d simply use this:
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wp_enqueue_script(‘jquery-color’);
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To include a script and specify the source, try this for including the jQuery Cycle plugin in the <head>:
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wp_enqueue_script(‘jquery-cycle’, ‘URL’, array(‘jquery’), ‘1.3.2’);
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The URL should not be a hard-coded value for local scripts. Refer to the Function Reference pages in the codex for proper URL formats for plugins and themes.
Register Your Scripts First
Make sure that your scripts are registered first before calling them. Registering a script basically tells WordPress where to find the code for your script. Use the function wp_register_script() to specify the location and handle of your script. The format is similar to the wp_enqueue_script() function:
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wp_register_script(‘$handle’, ‘$src’, ‘$deps’, ‘$ver’, ‘$in_footer’);
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The parameters have the same meanings and default values as used with wp_enqueue_script(). When in doubt, see what the WordPress Codex has to say about wp_enqueue_script() and wp_register_script().
Create a Function for the Header
Put it all together using wp_register_script(), wp_enqueue_script(), and the appropriate action to call the functions. Create a simple function, like id_scripts() below, and use the add_action() hook to queue up the scripts.
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function id_scripts() {
wp_register_script(‘script_alpha’, ‘URL’, array(‘jquery’), ‘1.0’);
wp_enqueue_script(‘script_alpha’);
}
add_action(‘wp_enqueue_scripts’, ‘id_scripts’);
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As a side note jQuery itself doesn’t have to be queued via a statement like wp_enqueue_script('jquery');, because it is listed as a dependency of ‘script-alpha‘ in this case.
When enqueuing a custom script that depends on a jQuery plugin, specify jQuery and its plugin in the $deps parameter of the wp_register_script() action for the custom script. For example, if your custom script depends on the jQuery Cycle plugin, which itself depends on jQuery, use array('jquery', 'jquery-cycle') for the $deps parameter. This specifies that both jQuery and its plugin Cycle should be loaded (in that order) before the custom script.
Place this code in the header.php of your theme. Remember, first register the javascript file, then enqueue it and make sure this is done before the wp_head(); statement. Your custom script can then be placed in header.php after the wp_head() call.
Use Theme functions.php to Safely Reference Your Script
When using a child theme take note that the header.php in a child theme will override the default header.php in the parent theme. Instead of placing the script-queuing code in the header, one could more safely put this code in functions.php. The advantage to that way is that the functions.php of a child theme is processed before the functions.php of the parent theme. Both the parent and child theme functions.php are processed, unlike header.php files.
If you’re the least bit unsure about messing with header.php, then just use functions.php to queue up your javascript files. Don’t forget the opening and closing PHP tags in functions.php, else it won’t work. Put the javascript that would come after the wp_head() call in a separate .js file in the child theme and you’re good to go.
Verify that everything is working correctly by viewing the source of the HTML document for a WordPress post that should have the script included. The <script> tags should be visible in the header or in the footer depending on how the scripts were called.