Convert old NodeJs applications to ES6 modules

23 Dec 2021 Matteo Mattei nodejs

Nowadays every Nodejs application should be converted to ES6 module because it brings several benefits:

• Modules may be executed any number of times, but are loaded only once, thus improving performance.
• Module scripts may be shared by multiple applications.
• Modules help identify and remove naming conflicts.

The biggest difference between standard javascript library and an ES6 module is how we include a library (which can be either within your project or external). The standard classic way is to use const library = require(‘library-name’) but with ES6 modules we have to use import library from ‘library-name’.

In order to support the import keyword you have to add the following line to the package.json of your application:

"type": "module"

In this way you are telling npm that your application is a pure ES6 module.

Then you have to change all require(xxx) statements with import xxx from ‘yyy’. In case you want to use an external library which is not a pure ES6 module you can always include it with this syntax:

import theNameYouWant from 'official-library-name'

In case you want to use a library which is placed inside your application you can use this syntax:

import theNameYouWant from './path/to/mylibrary.js'

And mylibrary.js can export a default object with all functions like this:

import axios from 'axios';

export default {
	run: function(){
		console.log('run');
	},
	sum: function(x, y){
		console.log(`Sum is ${x+y}`);
	},
	get: async function(){
		return await axios.get('https://github.com/matteomattei/matteomattei.github.io/raw/master/public/logo_professtional.jpg');
	}
}

And can be used in this way:

import mylib from './path/to/mylibrary.js'

mylib.run(); // prints 'run'
mylib.sum(2,3); // prints 'Sum is 5';
let getResult = await mylib.get();
console.log(Buffer.from(getResult.data).length); // prints the size of the image

You can also export single functions from your library like this:

import axios from 'axios';

export function run() {
  console.log("run");
}
export function sum(x, y) {
  console.log(`Sum is ${x + y}`);
}
export async function get() {
  return await axios.get(
    "https://github.com/matteomattei/matteomattei.github.io/raw/master/public/logo_professtional.jpg"
  );
}

In this case you have to use it in this way:

import * as mylib from './path/to/mylibrary.js'

mylib.run(); // prints 'run'
mylib.sum(2,3); // prints 'Sum is 5';
let getResult = await mylib.get();
console.log(Buffer.from(getResult.data).length); // prints the size of the image

Otherwise you can selectively import only the function you need:

import {run, sum, get} from './path/to/mylibrary.js'

run(); // prints 'run'
sum(2,3); // prints 'Sum is 5';
let getResult = await get();
console.log(Buffer.from(getResult.data).length); // prints the size of the image

Remember:

• You have to add type: “module” to your package.json file.
• You can use await directly in your main module without a wrap of an async function.
• Your code must be implicitly strict.