coroutine-fengari.js

// Import some stuff from fengari
global.WEB = false
const {
  lua: {
    lua_pushnil,
    lua_tointeger,
    lua_touserdata,
    lua_atnativeerror,
    lua_yield,
    lua_resume,
    lua_pushjsfunction,
    lua_setglobal,
    lua_pushliteral,
    to_luastring
  },
  lauxlib: {
    luaL_newstate,
    luaL_loadstring
  },
  lualib: {
    luaL_openlibs
  }
} = require('fengari')

// Define some custom global functions
const api = {
  // Used to test returning values from custom native functions
  hello (L) {
    lua_pushliteral(L, 'Hello World')
    return 1
  },
  // Used to test pausing and resuming a coroutine.
  delay (L) {
    setTimeout(() => {
      lua_resume(L, null, 0)
    }, lua_tointeger(L, -1))
    return lua_yield(L, 0)
  },
  // Another example, but promise based
  delay2 (L) {
    return pwait(L, pdelay(lua_tointeger(L, -1)))
  }
}

function pwait (L, promise) {
  promise.then(res => {
    lua_pushliteral(L, res)
    lua_resume(L, null, 1)
  }).catch(err => {
    lua_pushnil(L)
    lua_pushliteral(L, '' + err)
    lua_resume(L, null, 2)
  })
  return lua_yield(L, 0)
}

function pdelay (ms) {
  return new Promise(resolve => setTimeout(resolve, ms))
}

function main () {
  // Create a new state with default globals
  let L = luaL_newstate()
  luaL_openlibs(L)

  // Inject API functions into globals
  for (let key in api) {
    lua_pushjsfunction(L, api[key])
    lua_setglobal(L, to_luastring(key))
  }

  // Report native errors
  lua_atnativeerror(L, L => {
    console.error(lua_touserdata(L, 1))
    return 1
  })

  // Run some lua code in a coroutine
  luaL_loadstring(L, to_luastring(`
    print(hello())
    print "Starting Delay"
    for i=1,10 do
      delay(100)
      print "tick"
    end
    delay2(300)
    print "tock!"
  `))
  lua_resume(L, null, 0)
}

main()