How to use Espruino with WS2812 arrays? (Like RGB-123)

My WS2812's seem to be working okay too on new firmware.

Are you using a bare WS2812, as opposed to one included as part of a matrix or on a breakout board? If you're using a bare WS2812, did you remember the 0.1uf bypass capacitor? Without that, the WS2812 will turn itself off if you try to light it with a bright color (the exact point at which this happens depends on the physical parameters of your setup).