> AFAIK [there] is no good way to load a script at runtime and get an [event] when the file is loaded and parsed.

You can do this easily by creating a script element dynamically and then either:

1) Listen for the load event on that element, or

2) Have the dynamic script call a function that is already loaded.

Here is an example of the first technique:

  let script = document.createElement( 'script' );
  script.addEventListener( 'load', () => {
      alert( 'three.js is loaded: ' + THREE );
  });
  script.src = 'https://ajax.googleapis.com/ajax/libs/threejs/r84/three.min.js';
  document.head.appendChild( script );

https://jsfiddle.net/geary/szmc1L0h/9/

Thanks, I use this techinque but I had issues with it in the past, I tried a few minutes now to find documentation to confirm if the onload guarantees the script is loaded and finished parsing/interpreting but I can't find it.

Your example code works in all the browsers I tested so maybe it was an issue ith th particular script I was testing, there are third party scripts like for embedding an image editor, those could also use this trick to load some dependencies.

Great. so I was wrong then, this should work with most third party scripts.