Compiler from Go to JavaScript for running Go code in a browser
GopherJS compiles Go code to pure JavaScript code. Its main purpose is to give you the opportunity to write front-end code in Go which will still run in all browsers. Nearly everything is supported, including Goroutines (compatibility documentation). Performance is quite good in most cases, see HTML5 game engine benchmark. Cgo is not supported. GopherJS requires Go 1.16 or newer.
MultiWorld Explorer is an environment for all web-based internet games. They idea behind it is to add missing functionality to the game interface by running custom JScript code. This could be performed by anyone who can deal with JavaScript code.