A safer way to build robust
front-end web applications!


Strong typing guarantees your code is free of silly mistakes; no more mixing up strings or numbers, forgetting what keys an object has, or worrying about typos in your method names. Scala.js takes care of all this tedious book-keeping for you, letting you focus on the actual, more interesting problem your application is trying to solve.


Scala.js optimizes your Scala code into highly efficient JavaScript. Incremental compilation guarantees speedy (1-2s) turn-around times when your code changes. The generated JavaScript is both fast and small, starting from 45kB gzipped for a full application.


Scala.js loves JavaScript libraries, including React and AngularJS. You can use any JavaScript library right from your Scala.js code, either in a statically or dynamically typed way. You won't even notice you're crossing a language border! Learn more.

Excellent editor support

With Scala.js, typos and type-errors are immediately caught and shown to you in your editor, without even needing to compile your code. Refactor any field or method with ease, with the confidence that if you mess it up the editor will tell you immediately. Stop flipping back and forth between your editor and MDN, because your editor will display what methods are available, what arguments they take, what they return, and even their documentation, right in-line with your code!

Go beyond JavaScript ES6, today

Hello World!
ECMAScript 6
console.log("Hello World!");
println("Hello World!")
ECMAScript 6
class Person {
  constructor(firstName, lastName) {
    this.firstName = firstName;
    this.lastName = lastName;

  fullName() {
    return `${this.firstName} ${this.lastName}`;
class Person(val firstName: String, val lastName: String) {
  def fullName(): String =
    s"$firstName $lastName"
Fat arrow functions
ECMAScript 6
const names = => p.firstName);
val names = => p.firstName)
// or an even shorter version
val names =
ECMAScript 6
const personMap = new Map([
  [10, new Person("Roger Moore")],
  [20, new Person("James Bond")]
const names = [];
for (const [key, person] of personMap) {
  if (key > 15) {
    names.push(`${key} = ${person.firstName}`);
val personMap = Map(
  10 -> new Person("Roger Moore"),
  20 -> new Person("James Bond")
val names = for {
  (key, person) <- personMap
  if key > 15
} yield s"$key = ${person.firstName}"

To find out more about what Scala.js looks like for JavaScript developers, check out the detailed comparisons. If you want to try it out yourself, check out the Tutorials!

Feature JavaScript ES5 JavaScript ES6 TypeScript Scala.js
Fully EcmaScript5 compatible
No compilation required
Use existing JS libraries
Language features
Classes with inheritance
Support for types
Strong type system
Extensive standard libraries
Optimizing compiler
Macros, to extend the language
IDE support
Catch most errors in IDE
Easy and reliable refactoring
Reliable code completion