WP Deferred JavaScripts

This plugin defer the loading of all JavaScripts added by the way of wp_enqueue_script(), using LABJS. The result is a significant optimization of loading time.

It is compatible with all WordPress JavaScript functions (wp_localize_script(), js in header, in footer…) and works with all well coded plugins.

If a plugin or a theme is not properly enqueuing scripts, your site may not work. Check this page: Function Reference/wp_enqueue_script on WordPress Codex.

LABjs (Loading And Blocking JavaScript) is an open-source (MIT license) project supported by Getify Solutions.

We performed a range of tests to determine the potential benefit of loading time. On wabeo we executed webwait (150 calls by test). Result is this plugin could improve your loading time by 25%!!
More information in the Screenshots section.

You can find more information about WP Deferred JavaScripts and technical information about asynchronous scripts on authors blogs.

1. Upload the WP Deferred JavaScripts plugin to your blog and activate it.

2. Enjoy ^^

1. 

   Average load time of 1.91 seconds without WP Deferred JavaScripts activated and scripts loaded in the header

2. 

   Average load time of 1.99 seconds without WP Deferred JavaScripts activated and scripts queued in the footer

3. 

   Average load time of 1.56 seconds with WP Deferred JavaScripts activated and scripts queued in the header

4. 

   Average load time of 1.54 seconds with WP Deferred JavaScripts activated and scripts queued in the footer

WP Deferred JavaScript includes some hooks. If you never used one of them, check this page. It’s better to use those filters in a plugin or a mu-plugin.

Exclude Scripts

do_not_defer is a filter that took as a parameter an array containing scripts that should be handle normally.

Here is an example:

// Normal script enqueue.
add_action( 'wp_enqueue_scripts', 'register_canvas_script' );
function register_canvas_script() {
    wp_register_script( 'my-canvas-script', 'http://exemple.com/myscript.js' );
    wp_enqueue_script( 'my-canvas-script' );
}

// Don't defer this script.
add_filter( 'do_not_defer', 'exclude_canvas_script' );
function exclude_canvas_script( $do_not_defer ) {
    $do_not_defer[] = 'my-canvas-script';
    return $do_not_defer;
}

Since 2.0.3 you can also use the WP Deferred JS settings pannel!

Change LABJS URL

wdjs_labjs_src is a filter that allow you to change LabJS URL.
($lab_src, $lab_ver)

// for example, I need a specific version of LabJS
add_filter( 'wdjs_labjs_src', 'my_labjs_src', 10, 2 );
function my_labjs_src( $src, $ver ) {
    if ( '2.0' !== $ver ) {
        // Hotlinking raw github is a bad practice, I did it just for the lulz.
        return 'https://raw.githubusercontent.com/getify/LABjs/edb9fed40dc224bc03c338be938cb586ef397fa6/LAB.min.js';
    }
    return $src;
}

HTML5 compatibility

If you use HTM5, wdjs_use_html5 is a filter that remove the type="text/javascript" attribute. You can use it this way:

add_filter( 'wdjs_use_html5', '__return_true' );

Change a script URL

wdjs_deferred_script_src can be used to change the way one of the script is loaded. For example:

// Here, I need to add information about the charset.
add_filter( 'wdjs_deferred_script_src', '', 10, 3 );
function change_my_script_src( $src_string, $handle, $src ) {
    // $src_string -> .script("http://exemple.com/myscript.js?v=2.0")
    // $handle -> my-script
    // $src -> http://exemple.com/myscript.js?v=2.0
    $out = array( 'src' => $src, 'charset' => 'iso-8859-1' );
    return '.wait(' . json_encode( $out ) . ')';
}

How to execute a code right after script loading

You may need to execute a script right after its loading. You can use wdjs_deferred_script_wait filter to do it.

add_action( 'wdjs_deferred_script_wait', 'after_my_script', 10, 2 );
function after_my_script( $wait, $handle ) {
    if ( 'my-script' === $handle ) {
        $wait = 'function(){new MyScriptObject();}';
    }
    return $wait;
}

Execute a function when all scripts are loaded

You may have to use inline JavaScript in your footer. If that’s the case, you will have to use that last hook to make it compatible with WP Deferred JavaScripts.

You will have to wrap this inline JS into a new function. Then, you will have to use wdjs_before_end_lab to execute it.

// This is a fake function that we are wrapping in a new function
add_filter( 'before_shitty_plugin_print_js', 'wrap_this_code' );
function wrap_this_code( $code ) {
    return 'function PluginShittyCode(){' . $code . '}';
}

add_filter( 'wdjs_before_end_lab', 'call_shitty_code' );
function call_shitty_code( $end ) {
    $end .= '.PluginShittyCode()';
    return $end;
}

2.0.5

• Solve problem encountered on this support topic

2.0.4

• do_not_defer can now accept scripts URI.
• New settings sub-pannel to exclude scripts from deferring, without using the plugin filter.
• Tested up to WordPress 4.4.2

2.0.2

• Minor bugfix: now the plugin catches some data added lately and include it in the plugin script tag (instead of letting the data create its own tag).

2.0.1

• Small code improvement.
• Prefix functions with wdjs instead of sfdjs.

2.0.0

• Overall code rewrite, by Grégory Viguier.
• New hooks.
• LabJS is loaded now loaded asynchronously.
• Conditional script are now supported.
• Bug fix: 404 error on scripts without source.
• Script dependency that should not be deferred are now excluded automatically.
• WP Deferred JavaScripts is compatible with SF Cache Busting.

1.5.5

• Solve a problem when uri script contain “&”.
• Solve a bug while waiting dependencies.

1.5.4

• Prevent bug when scripts dependencies are not enqueued.

1.5.3

• Prevent a minor bug for footer enqueue script.

1.5.2

• Fixed a minor bug: bad priority while emptying $wp_scripts.

1.5.1

• Fixed a minor bug: plugin active was on login and register pages.

1.5

• Fixed a major bug: plugin active only in front end.

1.4

• Fixed a minor bug: some JavaScripts enqueued with very high priority were ignored – filter scripts are now hooked on wp_print_scripts.

1.3

• Fixed a major bug: files with dependencies are now waiting the loading of parent files before loading themselves.

1.2

• Data called after wp_head, but linked to a script queued into header are now considered by the plugin.

1.1

• Correction of some minor bugs
• Improve code readability

1.0

• Initial release