I am making an asynchronous single page application in Drupal 8. So far everything is working nicely. However, it has a lot of libraries that are needed for a lot of different things, depending on what the user decides to do.

The libraries are different depending on which content type is loaded. I want to only load the library ONCE when a user loads a content type for the first time.

Using the below code the library is attached every time the content type gets loaded. Leading to multiple instances of each library.

function mytheme_preprocess_node(&$variables) {
    $node = $variables['node'];
        case 'nodeone':
            $variables['#attached']['library'][] = 'mytheme/liba';
        case 'nodetwo':
            $variables['#attached']['library'][] = 'mytheme/libb';
        case 'nodethree':
            $variables['#attached']['library'][] = 'mytheme/libc';

I can't do a preproccess_page as the content types are loaded asynchronously and would imply loading everything at once. I can't attach the library to the twig template as again, it happens at the node level, not the page. I have tried to attach the library to a view template, but the same issue remains, it gets loaded multiple times.

If I could do some form of check to see if the library has already been loaded, I think that would be sufficient.

  • Seems you have to do this in your application then. The library loading.
    – leymannx
    Sep 5, 2018 at 11:53
  • Or switch off the asynchronism for the libraries part in your application.
    – leymannx
    Sep 5, 2018 at 11:58

1 Answer 1


EDIT: Sorry didn't see you were doing it via AJAX, my below example might not be the same. But the theory of the JS triggering multiple times rather than the actual files loading might still be valid

I don't think it's the piece of code you've showed is causing your issue. Is the library files definitely getting loaded multiple times into the source code? Or is it that the effects of the library are happening multiple times? (e.g. a JS being trgiggered multiple times) as thats a different issue

Drupal handles this situation and when it aggregates all the required libraries so any duplicates are removed. For example I'm just working on a news listing page that has 10 nodes coming out and just replicated your code to print "hi" add a library and the "hi" comes out 10 times but the library files only once

  • 1
    I think so too, the code shown is probably not causing the issue, more likely the content of the JS files. Especially for AJAX you have to follow strictly the documentation drupal.org/docs/8/api/javascript-api/javascript-api-overview
    – 4uk4
    Sep 5, 2018 at 12:04
  • Hey guys, thanks for the quick responses. The JS is running only once as I have everything setup in jQuery once functions, that part is fine.
    – user30360
    Sep 7, 2018 at 8:06
  • Hey guys, thanks for the quick responses. The JS is running only once as I have everything setup in jQuery once functions, that part is fine. The issue is that the corresponding library gets attached each time I load the content type. So if I open content type 'houses' 3 times, the JS only runs once (because of the jQuery once) but the library will have been loaded 3 times.It doesn't looks like the Ajax API in Drupal checks if it's already been loaded.
    – user30360
    Sep 7, 2018 at 8:13

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