I don't understand why SCRIPT elements doesn't have a "depends" attribute that list id names to other SCRIPT that must have finished before this script executes

I don't understand why SCRIPT elements doesn't have a "depends" attribute that list id names to other SCRIPT that must have finished before this script executes. Isn't that a huge issue if you intend to defer/async a script element for a js-library that other scripts depend on being there?