Nighttime Possum Meandering
    Have ideas to improve npm?Join in the discussion! »

    TypeScript icon, indicating that this package has built-in type declarations

    5.0.0 • Public • Published

    (wee) Entity Component System

    A tiny Entity Component System for Javascript


    • Super small & simple
    • Flexible - Use ECS or Observer pattern to interact with entities, any class can be a component.
    • Performant - Doesn't re-implement a GC, entities are deleted when they have no components and fall out of scope, avoids unnecessary iteration.


    yarn add wecs

    Quick Start

    For a more complete example, see the examples which don't exist yet

    import { World, ID, Component, getComponent } from 'wecs'
    // instantiate the world
    const world = new World()
    // create a component
    class Movable {} // Functions as a tag
    class Velocity extends Component<{ val: number }> { } // Use a shorthand generic base class
    class Position { // use your own class
      val: number
      constructor(pos) {
        this.val = pos
    // create a system that is called with entities every time is called
    function System(entities) {
      entities.forEach(e => {
        world.updateComponent(e, Position, c => {
          c.val += getComponent(e, Velocity).val
    // register the System to receive entities with both position and velocity components
    // create an entity, this one can move, has a position, and a velocity
      [ID, { id: 'foo' }],
      [Position, 0],
      [Velocity, { val: 2 }]
    // execute all systems in parallel



    World is the default export class containing entities

    constructor(config?: Config)

    You can construct World with the following config shape. All properties are optional.

    Key Type Description
    parallel boolean Run all systems in parallel
    id () => string Function used to generate entity IDs, defaults to a fast and good enough emplementation, but cuid would be good too if you prefer.
    onBefore (...args: any[]) => Promise<void> A function called with an optional message before all systems are run.`
    onAfter (...args: any[]) => Promise<void> A function called with an optional message after all systems are run.`

    addComponent<T>(entity: Entity, Component: Component<T>, ...args: any[])

    Add a single component to a given entity

    class Position {
      constructor(number, bar) {
        console.assert(number === 0)
        console.assert(foo === 'foo')
    world.addComponent(e, Position, 0, 'foo')

    addComponents(entity: Entity, components: [Component<unknown>, ...any[]][])

    Adds components to a given entity

        [Position, 0, 'foo'],
        [Velocity, 2, 'bar']

    createEntity(components: [Component<unknown>, ...any[]][]): Entity

    Creates an entity with the provided Components and values.

    class Velocity {
      constructor(number, bar) {
        console.assert(number === 2)
        console.assert(foo === 'bar')
    const entity = world.createEntity([
      [Position, 0, 'foo'],
      [Velocity, 2, 'bar']

    query(components: Component<unknown>[], persist?: Boolean): Entity[]

    Query all entities that meet the component criteria, optionally saving the query for faster retrieval later.

    const entities = world.query([Position, Velocity], true)

    register(system: Function, components: Component<unknown>[])

    Register a system function to be called with entities that meet all of the component criteria:

    class Component {
      constructor(counter) { = 'bar'
    function System(entities) {
      entities.forEach(e => world.updateComponent(e, Component, c => { = 'baz'
    world.register(System, [Component, OtherComponent, ThirdComponent])

    removeComponent<T>(entity: Entity, component: Component<T>)

    Removes a single component from a given entity


    removeComponents(entity: Entity, components: Component<unknown>[])

    Removes components from a given entity

      [Position, Velocity]

    async run(...args: any[]): Promise<void>

    Executes all the registered systems. If args are present (typically a ms delta of now minus last run, but can be whatever arguments you want), systems will be called with system(...args, entities) as opposed to just system(entities).

    function System(delta, time, entities) {
      // do stuff
    function run() {
      // Compute delta and elapsed time
      var time =
      var delta = time - lastTime
      // Run all the systems, time)
      lastTime = time
    var lastTime =

    Note: Dynamic length arguments passed to .run at runtime will likely fuxx with your program so try to stick to one function signature for all of your system functions. For example, the following is bad:

    // entities won't always be what you want it to be!
    function System(entities) {}
    function SystemTwo(delta, entities) {}
    // this sucks don't do this

    subscribe(components: Component<unknown>[], callback: QueryCallback, emit?: boolean): Function

    Subscribe to updates with a callback function that gets executed when:

    • a new entity meeting the component criteria gets created
    • an entity gets a new component that meets the criteria
    • an entity has a component removed that makes it no longer meet the criteria
    • an entity's component is updated via world.updateComponent

    The third emit argument, when true, will immediately call the callback with relevant entities.

    This method will also return a function you can use to unsubscribe.

    const unsubscribe = world.subscribe(
      [Position, Velocity],
      (entities) => console.log(entities),

    makeSubscription(components: IComponent<unknown>[], emit?: boolean): (cb: QueryCallback) => () => void

    Instead of taking a callback, create a factory function that can be used to create subscriptions. Returns a function that expects a single callback function as an argument that plays nicely with other reactive frameworks.

    var stream = Kefir.fromCallback(world.makeSubscription([Position, Velocity], true));
    // svelte
    function useEntities(components) {
      return {
        subscribe: world.makeSubscription(components, true)

    unsubscribe(components: Component<unknown>[], callback: QueryCallback)

    Another way to unsubscribe, handy for rxjs

    import { fromEventPattern } from 'rxjs';
    const addHandler = (components) => (handler) => {
      world.subscribe(components, handler, true)
    const removeHandler = (components) => (handler) => {
      world.unsubscribe(components, handler)
    const entities = fromEventPattern(
      addHandler([Position, Velocity]),
      removeHandler([Position, Velocity])
    entities.subscribe(entities => console.log(entities))

    updateComponent<T>(entity: Entity, Component, update: any | ComponentUpdater<T>):

    Takes an entity, a component, and a either callback function that is called with value of the entity's component, or a new value for the component.

    If the callback returns a value, the entity's component will be set to that value.

    Afterwards, trigger all relevant subscriptions

    class Component {
      constructor(multiplier = 2) {
        this.values = [1, 2, 3].map(v => v * multiplier)
    world.subscribe([Component], (entities) => {
      // this will be called three times
    const entity = world.createEntity([
      [Component, 1]
    world.updateComponent(entity, Component, c => {
      // mutate the component directly
      c.values = []
    world.updateComponent(e, Component, c => {
        // reset the value
      return new Component(3)
    // reset the value
    world.updateComponent(e, Component, new Component(3))


    The exported Component class is a generic class that expects to be constructed with an object of shape T, and assigns properties of the object T to its context.

    Component is mainly a convenient shorthand to build typed, easily serializable components.

    import { Component } from 'wecs'
    class Position extends Component<{ x: number, y: number }> { }
    const p = new Position({ x: 0, y: 0 })
    console.assert(p.x === 0)
    console.assert(p.y === 0)
    // You can easily serialize and reconstruct components this way
    console.assert(p.x === new Position(JSON.parse(JSON.stringify(p))).x)


    It's common practice when using ECS to uniquely identify your entities. The exported ID class extends Component and has elevated component privileges. Every entity is given an ID component, and ID components can not be removed from entities, but ID components can be updated.

    // Entities created without an ID component will use a short randomly generated id
    import { ID } from 'wecs'
    const entity = world.createEntity([Component])
    // Creating an entity with a custom ID component is fine too
    const entity = world.createEntity([
      [ID, { id: 'foo' }]
    getID(entity) === 'foo'

    getID(entity: Entity): string

    Retrieves a given entity's unique identifier from its ID component.

    const entity = world.createEntity([
      [ID, { id: 'foo' }]
    getID(entity) === 'foo'

    getComponent<T>(entity: Entity, Component: Component<T>): T

    Given an entity, gets the given component or null if the entity doesn't have it.

    import { getComponent } from 'wecs'
    const entity = world.createEntity([
      [Position, 0],
      [Velocity, 2]
    const position = getComponent(entity, Position)

    hasComponent<T>(entity: Entity, components: Component<T>)

    Given an entity, gets the given component or null if the entity doesn't have it.

    import { hasComponent } from 'wecs'
    const entity = world.createEntity([
      [Position, 0],
      [Velocity, 2]
    console.assert(hasComponent(entity, Position))

    hasComponents(entity: Entity, components: Component<unknown>[])

    Given an entity, gets the given component or null if the entity doesn't have it.

    import { hasComponents } from 'wecs'
    const entity = world.createEntity([
      [Position, 0],
      [Velocity, 2]
    console.assert(hasComponents(entity, [Position, Velocity]))


    npm i wecs

    DownloadsWeekly Downloads






    Unpacked Size

    117 kB

    Total Files


    Last publish


    • avatar