vectrexweb.js and vectrexweb.wasm are MAME 0.285, vectrex driver only, compiled to WebAssembly.
The picture is drawn by beam.js from MAME's beam output. It is not MAME's renderer.
Licence: GNU GPL version 2 or later. COPYING.
Source: MAME 0.285, with these changes:
Complete source on request: jaymz@sadenby.com.
vectrex.zip is the Vectrex system ROM, not part of MAME.