One way to make the new developers learn rapidly is by giving them adjusted challenges. If they tend to use a lot of jQuery, give them a task to solve which is easier without jQuery. They will probably use jQuery. Then tell them that they have to strip the jQuery in oder to save bytes. Give them enough time to come up with a solution. It should be a problem which can be solved easily with VanillaJS, ideally in fewer lines of code. My upcoming Hashnode Original article contains at least one example. The trick with this way is that they realize themselves that a library or framework is not always the best solution. Also you might make them work on bugs instead of new code, which requires them to read lots of internal code. Just using a framework, they might not be able to solve the bugs, so they will have to go deeper.
As for old developers, I do not have any experience, but I would demonstrate the technology to them with examples of tech they already use and love. Show them shortcomings and how new tech can help them. Old developers usually try to only use what is of benefit to them and don't care about hype, so you have to show them that the new tech really is useful and in what kind of situations it is. Try to have them come up with their own problem cases and try to find a solution with the new tech!