I don't know its current status with the committee, but https://github.com/tc39/proposal-frozen-realms https://github.com/tc39/proposal-frozen-realms proposes s

I don't know its current status with the committee, but https://github.com/tc39/proposal-frozen-realms https://github.com/tc39/proposal-frozen-realms proposes something equivalent to Caja for modern JS. It can be a lot simpler now because ES6+ is much closer to what's needed than JS was when Caja was made.