Compiling and bundling JavaScript, the painless way

Michele Riva

Michele Riva

Senior Software Architect @NearForm

Google Developer Expert

Microsoft MVP

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Real-World Next.js

Build scalable, high performances and modern web applications using Next.js, the React framework for production

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Compiling and bundling JavaScript

is (often) a pain*

*but it shouldn't

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A bit of terminology: compiling

to change a computer program into a machine language

Cambridge Dictionary

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A bit of terminology: compiling transpiling

to translate a source code into a different language source code

Me, myself

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A bit of terminology: bundling

to encapsulate code and resources into a single executable file

Me, myself

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Why do we want to transpile our code?

To make it compatible with different platforms
To write our scripts in different languages
To adopt new language features

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Scala.js

https://www.scala-js.org

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ReasonML

ReScript

F# (via Fable)

Gleam

Elm

Kotlin

Nim, Haxe, C/C++ (via Emscripten), ClojureScript, Dart, PureScript, Haskell (via GHCJS)

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LLVM

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function toUpper(x) {
  return x.toUpperCase();
}

function addExclamationMarks(x) {
  return x + '!!!'
}

function scream(input) {
  return input
    |> toUpper
    |> addExclamationMarks
    |> console.log
}

scream('Hello, Belgium');
// HELLO, BELGIUM!!!

"use strict";

function toUpper(x) {
  return x.toUpperCase();
}

function addExclamationMarks(x) {
  return x + '!!!';
}

function scream(input) {
  var _ref, _ref2, _input;

  return _ref = (
    _ref2 = (_input = input, toUpper(_input)),
    addExclamationMarks(_ref2)
  ), console.log(_ref);
}

scream('Hello, Belgium');
// HELLO, BELGIUM!!!

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import { VFC } from 'react';

enum UserType {
  ADMIN     = "admin",
  EDITOR    = "editor",
  USER      = "user",
  ANONYMOUS = "guest"
}

type MyProps = {
  userType: UserType;
}

const MyComponent: VFC<MyProps> = ({ userType }) => {
  return (
    <div>
      User is of type: {props.userType}
    </div>
  )
}

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
var UserType;

(function (UserType) {
  UserType["ADMIN"] = "admin";
  UserType["EDITOR"] = "editor";
  UserType["USER"] = "user";
  UserType["ANONYMOUS"] = "guest";
})(UserType || (UserType = {}));

const MyComponent = ({ userType }) => {
  return /*#__PURE__*/ React.createElement(
    "div",
    null,
    "User is of type: ",
    props.userType
  );
};

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Why do we want to bundle our code?

To create a single executable file
To serve a single JS file over the net

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ReadArticle.jsx

NewArticle.jsx

AuthorProfile.jsx

BundledPage.js

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in depths

transpiling

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Language-to-language

ClojureScript

(defn simple-component []
  [:div
   [:p "I am a component!"]
   [:p.someclass
    "I have " [:strong "bold"]
    [:span {:style {:color "red"}} " and red "] "text."]])

cljs.user.simple_component = (function cljs$user$simple_component(){
  return new cljs.core.PersistentVector(null, 3, 5, cljs.core.PersistentVector.EMPTY_NODE,
  [new cljs.core.Keyword(null,"div","div",(1057191632)),
  new cljs.core.PersistentVector(null, 2, 5, cljs.core.PersistentVector.EMPTY_NODE,
  [new cljs.core.Keyword(null,"p","p",(151049309)),"I am a component!"], null),
  new cljs.core.PersistentVector(null, 5, 5, cljs.core.PersistentVector.EMPTY_NODE,
  [new cljs.core.Keyword(null,"p.someclass","p.someclass",(-1904646929)),
  "I have ",new cljs.core.PersistentVector(null, 2, 5, cljs.core.PersistentVector.EMPTY_NODE, 
  [new cljs.core.Keyword(null,"strong","strong",(269529000)),"bold"], null),
  new cljs.core.PersistentVector(null, 3, 5, cljs.core.PersistentVector.EMPTY_NODE, 
  [new cljs.core.Keyword(null,"span","span",(1394872991)),
  new cljs.core.PersistentArrayMap(null, 1, [new cljs.core.Keyword(null,"style","style",(-496642736)),
  new cljs.core.PersistentArrayMap(null, 1, [
  new cljs.core.Keyword(null,"color","color",(1011675173)),"red"]
  , null)], null)," and red "], null),"text."], null)], null);
});

https://reagent-project.github.io

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[@bs.config {jsx: 3}];

module Greeting = {
  [@react.component]
  let make = () => {
    <button> {React.string("Hello!")} </button>
  };
};

ReactDOMRe.renderToElementWithId(<Greeting />, "preview");

// Generated by BUCKLESCRIPT, PLEASE EDIT WITH CARE
'use strict';

var React = require("react");
var ReactDOMRe = require("./stdlib/reactDOMRe.js");

function _none_$Greeting(Props) {
  return React.createElement("button", undefined, "Hello!");
}

var Greeting = {
  make: _none_$Greeting
};

ReactDOMRe.renderToElementWithId(React.createElement(_none_$Greeting, { }), "preview");

exports.Greeting = Greeting;
/*  Not a pure module */

https://reasonml.github.io

Language-to-language

ReasonML

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Language-to-language

TypeScript

import { VFC } from 'react';

enum UserType {
  ADMIN     = "admin",
  EDITOR    = "editor",
  USER      = "user",
  ANONYMOUS = "guest"
}

type MyProps = {
  userType: UserType;
}

const MyComponent: VFC<MyProps> = ({ userType }) => {
  return (
    <div>
      User is of type: {props.userType}
    </div>
  )
}

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
var UserType;

(function (UserType) {
  UserType["ADMIN"] = "admin";
  UserType["EDITOR"] = "editor";
  UserType["USER"] = "user";
  UserType["ANONYMOUS"] = "guest";
})(UserType || (UserType = {}));

const MyComponent = ({ userType }) => {
  return /*#__PURE__*/ React.createElement(
    "div",
    null,
    "User is of type: ",
    props.userType
  );
};

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Every language has its own transpiler

TypeScript TSC

Fable

ClojureScript

BuckleScript

JavaScript (Babel)

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Problem #1

transpilation time

Really fast

Average

Fast

Slow on large codebases

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Problem #2

optimized output

Beautifully optimized

Awful

Beautifully optimized

Quite optimized

Well optimized*

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Let's focus on the most popular ones

Quite slow, quite optimized

Quite fast, well optimized*

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Bundling time grows

Quite slow, quite optimized

Quite fast, well optimized

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in depths

bundling

WebPack

Parcel

Rollup

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Hard

Easier

Easiest

WebPack

Parcel

Rollup

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Hard

Easier

Easiest

Slowest

Slower

Fast

WebPack

Parcel

Rollup

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king of configurations

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king of configurations

Is it still worth it?

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ESBuild

SWC

Vite

Snowpack

is there any better alternative?

(rest in pepperoni)

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esbuild src/myEntry.js --bundle --sourcemap --minify --outfile=dist/mybundle.js

ESBuild

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ES2019

ES2020

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{
  "jsc": {
    "parser": {
      "syntax": "ecmascript",
      "jsx": false,
      "dynamicImport": false,
      "privateMethod": false,
      "functionBind": false,
      "exportDefaultFrom": false,
      "exportNamespaceFrom": false,
      "decorators": false,
      "decoratorsBeforeExport": false,
      "topLevelAwait": false,
      "importMeta": false
    },
    "transform": null,
    "target": "es5",
    "loose": false,
    "externalHelpers": false,
    // Requires v1.2.50 or upper and requires target to be es2016 or upper.
    "keepClassNames": false
  }
}

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SWC can run in a browser thanks to WASM

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Vite

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Vite

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Vite

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// ESM
export default function greet() {
  return "Hello Serbia!";
}

// ESM
import foo, { bar } from "foobar";

// CJS
module.exports = function greet() {
  return "Hello Serbia!";
}

// CJS
const foo, { bar } = require("foobar");

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Vite

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rest in pepperoni

Snowpack

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Snowpack

rest in pepperoni

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Snowpack

rest in pepperoni

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/*
 * Skypack CDN - canvas-confetti@1.4.0
 *
 * Learn more:
 *   📙 Package Documentation: https://www.skypack.dev/view/canvas-confetti
 *   📘 Skypack Documentation: https://www.skypack.dev/docs
 *
 * Pinned URL: (Optimized for Production)
 *   ▶️ Normal: https://cdn.skypack.dev/pin/canvas-confetti@v1.4.0-POmgSMO0U5q84otJfYlN/mode=imports/optimized/canvas-confetti.js
 *   ⏩ Minified: https://cdn.skypack.dev/pin/canvas-confetti@v1.4.0-POmgSMO0U5q84otJfYlN/mode=imports,min/optimized/canvas-confetti.js
 *
 */

// Browser-Optimized Imports (Don't directly import the URLs below in your application!)
export * from '/-/canvas-confetti@v1.4.0-POmgSMO0U5q84otJfYlN/dist=es2020,mode=imports/optimized/canvas-confetti.js';
export {default} from '/-/canvas-confetti@v1.4.0-POmgSMO0U5q84otJfYlN/dist=es2020,mode=imports/optimized/canvas-confetti.js';

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The future is no-bundle

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The future is no-bundle*

*maybe

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The future is bright

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https://kdy1.dev/posts/2022/1/tsc-go

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@MicheleRiva

@MicheleRivaCode

/in/MicheleRiva95

www.micheleriva.dev