I'm trying to make JS and CSS asynchronous without plugins(I know this is possible, without much of coding).

As I'm not really know php, I would like you to help me a little bit over here.

I found this code, to handle this kind of thing, but I don't really understand how to use it.

function add_async_attribute($tag, $handle) {
   $scripts_to_async = array('my-js-handle', 'another-handle');
   foreach($scripts_to_async as $async_script) {
      if ($async_script !== $handle) return $tag;
      return str_replace(' src', ' async="async" src', $tag);
   return $tag;
add_filter('script_loader_tag', 'add_async_attribute', 10, 2);

What should I place exactly instead of my-js-handle or another-handle if JQuery file placed here: wordpress/wp-includes/js/jquery/jquery.js?ver=1.11.3 ?

Also, if I'll enlarge the array, say like this:

array('my-js-handle', 'another-handle', 'one-more');

Would I need to change something, say this(in the end of add_filter): 10, 2); ?

And as for the css asynchronization... would it be enough to simply enlarge this array and add mine css address?

1 Answer 1


You would use the handle of your enqueued scripts, ie, the first parameter of the wp_enqueue_script function used in WordPress for all your scripts... (if you are loading them another way you should use this function instead.)

The handle for jQuery is... jquery actually jquery-core now. But each script queued will have it's own handle. A bit like a 'slug' for a post.

You are fine to add as many handles to that array without having to change the filter parameters. (The 10, 2 part is the filter run priority and number of arguments passed to the filter function respectively.)

But the script_loader_tag filters enqueued scripts, not stylesheets, so no this will not be fine for doing the same with CSS files.

EDIT I don't think that loop will work as it is, as it will return on the first fail, and thus not check all the handles. Use instead:

foreach($scripts_to_async as $async_script) {
  if ($async_script === $handle) {return str_replace(' src', ' async="async" src', $tag);}
  • Thank you. Could you please tell me, how should I implement this if I have plugin that load JavaScripts to be async.? I found a file in the plugins folder, and there's couple of wp_enqueue_script in it. As I understand this is the exact code that load the necessary "<scripts>". I tried to add in my array(in functions.php of my theme) this names of the plugin's wp_enqueue_script, but this didn't work.
    – tosananuco
    Apr 6, 2016 at 5:23
  • yes the first argument is the handle, ie. wp_enqueue_script($handle,$url...... your array should just contain a list of those strings. if it is not working something else is wrong... ah. see edit.
    – majick
    Apr 6, 2016 at 5:30
  • Thanks, but this still not working. I tried it like that: function add_async_attribute($tag, $handle) { $scripts_to_async = array('jquery'); foreach($scripts_to_async as $async_script) { if ($async_script === $handle) {return str_replace(' src', ' async="async" src', $tag);} } return $tag; } add_filter('script_loader_tag', 'add_async_attribute', 10, 2);
    – tosananuco
    Apr 6, 2016 at 5:39
  • ah whoops my bad actually, the jquery handle is a combined dependency handle that includes jquery-core and jquery-migrate... so just change the array value to jquery-core
    – majick
    Apr 6, 2016 at 6:54

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