What is Javelin?

Javelin is an Entity Component System (ECS) framework for TypeScript and JavaScript. It draws inspiration from other ECS frameworks like Bevy and Flecs to provide an ergonomic, performant, and interoperable way of creating games in JavaScript.


Systems with reactive entity queries.

let lootSystem = () => {
  world.query(Player).each((player, playerBox) => {
    world.query(Loot).each((loot, lootBox) => {
      // (pick up loot bag)

A scheduler with run criteria, ordering constraints, and system groups.

let weatherEnabled = (world: j.World) => {
  return world.getResource(Config).weatherEnabled
  .addSystem(lootSystem, j.after(shootSystem))
  .addSystem(weatherSystem, null, weatherEnabled)
  .addSystemToGroup(j.Group.Late, renderSystem)

A type system used to create, add, and remove sets of components from entities.

let Transform = j.type(Position, Rotation, Scale)
let Mesh = j.type(Geometry, Material)
let Player = j.type(Transform, Mesh)


Enum components used to safeguard entity composition and implement state machines.

let PlanetType = j.slot(Gas, Rock)
// Error: An entity can have at most one component for a given slot
world.create(j.type(PlanetType(Gas), PlanetType(Rock)))

Entity relationships with built-in support for heirarchies.

let parent = world.create()
let child = world.create(j.ChildOf(parent))
world.delete(parent) // also deletes `child`

And much more! Move to the next chapter to learn how to install Javelin.