This package aims to provide a way to:
- Embed Lua to any Node.js, Deno or Web Application.
- Run lua code in any operational system
- Interop Lua and JS without memory leaks (including the DOM)
To initialize, create a new Lua state, register the standard library, set a global variable, execute a code and get a global variable:
const { LuaFactory } = require('wasmoon')
// Initialize a new lua environment factory
// You can pass the wasm location as the first argument, useful if you are using wasmoon on a web environment and want to host the file by yourself
const factory = new LuaFactory()
// Create a standalone lua environment from the factory
const lua = await factory.createEngine()
try {
// Set a JS function to be a global lua function
lua.global.set('sum', (x, y) => x + y)
// Run a lua string
await lua.doString(`
print(sum(10, 10))
function multiply(x, y)
return x * y
end
`)
// Get a global lua function as a JS function
const multiply = lua.global.get('multiply')
console.log(multiply(10, 10))
} finally {
// Close the lua environment, so it can be freed
lua.global.close()
}Although Wasmoon has been designed to be embedded, you can run it on command line as well, but, if you want something more robust on this, we recommend to take a look at demoon.
$: wasmoon [options] [file] [args]Available options are:
-l: Include a file or directory-i: Enter interactive mode after running the files
$: wasmoon -i sum.lua 10 30And if you are in Unix, you can also use it as a script interpreter with Shebang:
#!/usr/bin/env wasmoon
return arg[1] + arg[2]$: ./sum.lua 10 30Wasmoon compiles the official Lua code to webassembly and creates an abstraction layer to interop between Lua and JS, instead of fengari, that is an entire Lua VM rewritten in JS.
Because of wasm, wasmoon will run Lua code much faster than fengari, but if you are going to interop a lot between JS and Lua, this may be not be true anymore, you probably should test on you specific use case to take the prove.
This is the results running a heap sort code in a list of 2k numbers 10x(less is better):
| wasmoon | fengari |
|---|---|
| 15.267ms | 389.923ms |
Fengari is smaller than wasmoon, which can improve the user experience if in web environments:
| wasmoon | fengari | |
|---|---|---|
| plain | 393kB | 214kB |
| gzipped | 130kB | 69kB |
Bundle/require errors can happen because wasmoon tries to safely import some node modules even in a browser environment, the bundler is not prepared to that since it tries to statically resolve everything on build time. Polyfilling these modules is not the right solution because they are not actually being used, you just have to ignore them:
Add the resolve.fallback snippet to your config:
module.exports = {
entry: './src/index.js', // Here is your entry file
resolve: {
fallback: {
path: false,
fs: false,
child_process: false,
crypto: false,
url: false,
module: false,
},
},
}With the package rollup-plugin-ignore, add this snippet to your config:
export default {
input: 'src/index.js', // Here is your entry file,
plugins: [ignore(['path', 'fs', 'child_process', 'crypto', 'url', 'module'])],
}Add the section browser on package.json:
{
"main": "src/index.js",
"browser": {
"child_process": false,
"fs": false,
"path": false,
"crypto": false,
"url": false,
"module": false
}
}Firstly download the lua submodule and install the other Node.JS dependencies:
git submodule update --init # download lua submodule
npm i # install dependenciesYou need to install docker and ensure it is on your PATH.
After cloned the repo, to build you just have to run these:
npm run build:wasm:docker:dev # build lua
npm run build # build the js code/bridge
npm test # ensure everything it's working fineYou need to install emscripten and ensure it is on your PATH.
After cloned the repo, to build you just have to run these:
npm run build:wasm:dev # build lua
npm run build # build the js code/bridge
npm test # ensure everything it's working finenull is injected as userdata type if injectObjects is set to true. This works as expected except that it will evaluate to true in Lua.
Promises can be await'd from Lua with some caveats detailed in the below section. To await a Promise call :await() on it which will yield the Lua execution until the promise completes.
const { LuaFactory } = require('wasmoon')
const factory = new LuaFactory()
const lua = await factory.createEngine()
try {
lua.global.set('sleep', (length) => new Promise((resolve) => setTimeout(resolve, length)))
await lua.doString(`
sleep(1000):await()
`)
} finally {
lua.global.close()
}It's not possible to await in a callback from JS into Lua. This is a limitation of Lua but there are some workarounds. It can also be encountered when yielding at the top-level of a file. An example where you might encounter this is a snippet like this:
local res = sleep(1):next(function ()
sleep(10):await()
return 15
end)
print("res", res:await())Which will throw an error like this:
Error: Lua Error(ErrorRun/2): cannot resume dead coroutine
at Thread.assertOk (/home/tstableford/projects/wasmoon/dist/index.js:409:23)
at Thread.<anonymous> (/home/tstableford/projects/wasmoon/dist/index.js:142:22)
at Generator.throw (<anonymous>)
at rejected (/home/tstableford/projects/wasmoon/dist/index.js:26:69)
Or like this:
attempt to yield across a C-call boundary
You can workaround this by doing something like below:
function async(callback)
return function(...)
local co = coroutine.create(callback)
local safe, result = coroutine.resume(co, ...)
return Promise.create(function(resolve, reject)
local function step()
if coroutine.status(co) == "dead" then
local send = safe and resolve or reject
return send(result)
end
safe, result = coroutine.resume(co)
if safe and result == Promise.resolve(result) then
result:finally(step)
else
step()
end
end
result:finally(step)
end)
end
end