This is not helpful.
That said, I believe he is asking about "emulators" like EmulationJS/similar, such as clients like RomM implement. As far as I'm aware, there are no javascript Dreamcast emulators and frankly there are unlikely to be anytime soon due to the performance of such things. Projects like RomM (utilizing EmulatorJS) are cool for simpler systems though, like the 16-bit era or earlier. Anything newer (N64, PS1, Saturn) than that is technically supported, but worthless due to performance IMHO.