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How to defer parsing JavaScript in WordPress

It’s a good practice to delay parsing JavaScript until the page content is loaded. This will improve the page speed and offers a better user experience.

There are two HTML attributes you can use to defer JavaScript: defer and async.

<!-- async attribute -->
<script src= “path/to/script” async> </script>

<!-- defer attribute -->
<script src= “path/to/script” defer> </script>

In WordPress, scripts are not added directly to the HTML markup, instead, we use built-in functions to do that for us. So it can be a little bit tricky to add the two attributes to the script tags. Thankfully, we can always rely on the functions.php file to fix that. Here is the script:

* Add this to functions.php file

# the attributes are passed by the "script_loader_tag" hook
function defer_scripts(
    $tag, # The <script> tag for the enqueued script
    $handle, # The script's registered handle
    $src # The script's source URL
    // The handles of the enqueued scripts we want to defer
    $defer_scripts = [

    if (in_array($handle, $defer_scripts)) {
	return '<script src="' . $src . '" defer="defer"></script>' . "\n";

    return $tag;
# Filter the HTML script tag of an enqueued script.
# '3' stands for 3 arguments to be passed to the "defer_scripts" callback
add_filter( 'script_loader_tag', 'defer_scripts', 10, 3); 
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