Fengari

What is it?

Fengari (Moon in greek) is the Lua VM written in JavaScript. It uses JavaScript's garbage collector so that interoperability with the DOM is non-leaky.

It comes with a simple module, that renders any interaction with JavaScript and the DOM transparent:

local js = require "js"
local window = js.global

window:alert("Hello from Fengari!")

local js = require "js"
local window = js.global
local document = window.document

print("Document's title: " .. document.title)

Lua in the browser means you can use coroutines to write beautiful asynchronous code:

local js = require "js"
local window = js.global

local function sleep(delay)
    local co = assert(coroutine.running(), "Should be run in a coroutine")

    window:setTimeout(function()
        assert(coroutine.resume(co))
    end, delay*1000)

    coroutine.yield()
end

coroutine.wrap(function()
    print "Going to sleep now..."

    sleep(3)

    print "Sleep well?"
end)()

Test it out!

Fengari 0.1.4  Copyright (C) 2017-2018 B. Giannangeli, Daurnimator
Based on: Lua 5.3.4  Copyright (C) 1994-2017 Lua.org, PUC-Rio

Getting started

The easiest way to get started with Fengari in the browser is to use fengari-web. This module will watch the DOM for any <script type="application/lua" src="..."> and run them with Fengari.

1. Download fengari-web:

   $ curl -L -O https://github.com/fengari-lua/fengari-web/releases/download/v0.1.4/fengari-web.js

2. Include it in your webpage:

   <script src="fengari-web.js" type="text/javascript"></script>

3. Now any script of type application/lua will be run by fengari:

   <script type="application/lua">
   print("hello world!")
   </script>
   
   <script src="/my-script.lua" type="application/lua" async></script>

Structure

Fengari is spread across several repositories:

• fengari: the core, largely a port of the PUC-Rio C implementation of Lua
• fengari-web: to use Fengari in the browser as easily as you might use JavaScript
• fengari-interop: a lua library that makes interoperating with JavaScript objects simple, it is already included in fengari-web
• fengari-node-cli: Lua CLI but running on top of Node.js
• fengari-loader: to bundle lua code as part of a webpack build process