Convenient way to use Babel syntax in Node.JS

#node #javascript #babel #express

When you want to use latest javascript syntax on the server side, typically you are offered two options: babel-node or the --experimental-modules flag.
In this post I want to share another convenient way to use Babel in server applications trough a small library called Pirates

Hijack require

Pirates lets you create your own module loaders for any file types trough a simple API. Among other cool things, It can be used to pre-compile javascript files written with latest ES features.

Consider following example:

const {addHook} = require('pirates');

function matcher(filename) {
  // Here, you can inspect the filename to determine if it should be hooked or not. Just return a truthy/falsey. Files in node_modules are automatically ignored, 
  // TODO: Implement your logic here
  return true;
}

const unregister = addHook(
  (code, filename) => code.replace('@@foo', 'console.log(\'foo\');'), 
  { exts: ['.js'], matcher }
);

// And later, if you want to un-hook require, you can just do:
// unregister();

addHook() accepts two arguments: 1. A parser callback 2. An object with options.

Setting up the project

Let's create an example ExpressJS project with Pirates.

1. Installing Dependencies:

mkdir pirates-test && cd pirates-test
npm init
npm i pirates @babel/preset-env @babel/core express

2. Add Babel hook

Create a file called nodeHooks.js with following content:


const {addHook} = require('pirates')
const {transform} = require('@babel/core')

module.exports = (options) => addHook(
  function(source, filename) {
    return transform(source, {
      presets: [
        [
          '@babel/preset-env',
          {
            modules: 'cjs',
            targets: {
              node: process.versions.node
            }
          }
        ]
      ]
    }).code
  },
  {
    exts: ['.js'],
    ignoreNodeModules: true,
    ...options
  }
)

As you can see the hook function is not so different from a .babelrc configuration.

3. Create an entry point for your application

Now before using Babel in the application we need to register the hook. Right way to do it would be to create an entry point for our application which would load all configurations and register hooks before running the server.

Create index.js with following content:

const registerHooks = require('./nodeHooks')
registerHooks()

// load some configs synchronously 
// then run the server

require('./server')

4. Write the application with Babel

Create server.js with following content:

import express from 'express'

const app = express()

app.get('/', (req, res) => {
    res.send('Hello world!')
})

app.listen(8080)

export default app