Escarole NPM | npm.io

Entity System Component library for typescript and javascript.

Installation

$ npm install escarole --save

Usage

Using components

This library requires that components are defined by classes or functions (the old style of doing object oriented style in Javascript).

Thus to define a you simply define a component class:

class VelocityComponent {
  constructor(
    public x: number,
    public y: number
  ) {}
}

class PositionComponent {
  constructor(
    public x: number,
    public y: number
  ) {}
}

Using an EntityManager

As an entity is comprised by components, we can create entities by first creating a EntityManager, and then invoking createEntity with the desired instantiate of components:

import {EntityManager} from `escarole`

const entityManager = new EntityManager()
 
let entity1 = entityManager.createEntity(new VelocityComponent(), new PositionComponent())
 
let entity2 = entityManager.createEntity(new PositionComponent())

Entities also be can be removed by deleteEntity with the desired entity on the EntityManager.

Iterating through all entities can be done via the getEntities method of the EntityManager:

// Iterate through all entities in the manager
for (let entity of entityManager.getEntities()) {
  // ...
}

// Select entities, which only has the both the PositionComponent and
// VelocityComponent (i.e. a entity with only a PositionComponent or
// VelocityComponent  will not be selected)
for (let entity of entityManager.getEntities(PositionComponent, VelocityComponent)) {
  // ...
}

A shorthand for iterating over all the entities is also available:

// This will iterate through all entities
for (let entity of entityManager) {
  // ...
}

Using an Entity

Once you have your hands on a Entity you can get one of its associated component by invoking getComponent on a entity. This will give you the associated component instance if the entity has one, or a value of undefined if it's not there:

for (let entity of entityManager) {
  let position = entity.getComponent(PositionComponent)
  if (position) {
    // Here we have selected entities with a position component
    position.x += 1
    position.y += 2
  }
}

// The previous loop is equivalent to the following loop

for (let entity of entityManager.getEntities(PositionComponent)) {
  let position = entity.getComponent(PositionComponent)
  position.x += 1
  position.y += 2
}

Like entities in a EntityManager, components can also be removed from an Entity or added to it:

for (let entity of entityManager.getEntities(PositionComponent)) {
  let position = entity.getComponent(PositionComponent)
  position.x += 1
  position.y += 2

  if (position.x > 10) {
    // suddenly the entity has velocity !
    entity.addComponent(new VelocityComponent())
  }
}

for (let entity of entityManager.getEntities(VelocityComponent, PositionComponent)) {
  // now the entities which has gained velocity will be considered here too
  let position = entity.getComponent(PositionComponent)
  let velocity = entity.getComponent(VelocityComponent)
  position.x -= 1 + velocity.x * 10
  position.y += 2 + velocity.y * 5

  if (position.x < 1) {
    // now our entity does not velocity anymore
    entity.deleteComponent(VelocityComponent)
  }
}

Using a System

System are the transform unit of a Entity Component System architecture. Escarole does not provide a specific abstraction to model a system. Rather, functions or methods are used to implement a system.