As a follow up comment I would say let the business requirements of a given client dictate the need for clearance. However, it takes so long to achieve a clearance it costs less to simply hired cleared people or pay for the clearance as a part of employee on-boarding.
If I were to do this as a real business I would always impose formal language training in the JavaScript language, so prior JavaScript experience is a largely irrelevant indicator of compatibility. That is because experiences writing the language professionally vary wildly in the market place and quality of code authorship is exceedingly rare. Producing high quality output is not challenging, but most people doing this for a job completely lack proper guidance or shouldn't be there in the first place.
Therefore the most ideal candidates are people who can be trained to a very high standard. I would filter for that first and then optionally filter for clearance secondly. You will be investing in these people so be choosy by potential, intelligence, writing skills, and organizational capacity.
