Loader.prototype.load doesn't check GetOrCreateLoad

[guybedford]

This will cause a TypeError:

  // preload jquery
  System.load('jquery');

  // preload jquery again (just in case)
  System.load('jquery');
  // -> TypeError!

[guybedford]

Note that this is a valid use case, because I might want to attach any number of load callbacks knowing when a tree has loaded, without necessarily executing.

[guybedford]

Duplicate.