jecs/docs/api/world.md

World

A World contains entities which have components. The World is queryable and can be used to get entities with a specific set of components and to perform different kinds of operations on them.

Functions

new

World utilizes a class, meaning JECS allows you to create multiple worlds.

function World.new(): World

Example:

::: code-group

local world = jecs.World.new()
local myOtherWorld = jecs.World.new()

import { World } from "@rbxts/jecs";

const world = new World();
const myOtherWorld = new World();

:::

Methods

entity

Creates a new entity.

function World:entity(): Entity

Example:

::: code-group

local entity = world:entity()

const entity = world.entity();

:::

component

Creates a new component. Do note components are entities as well, meaning JECS allows you to add other components onto them.

These are meant to be added onto other entities through add and set

function World:component<T>(): Entity<T> -- The new componen.

Example:

::: code-group

local Health = world:component() :: jecs.Entity<number> -- Typecasting this will allow us to know what kind of data the component holds!

const Health = world.component<number>();

:::

get

Returns the data present in the component that was set in the entity. Will return nil if the component was a tag or is not present.

function World:get<T>(
    entity: Entity, -- The entity
    id: Entity<T> -- The component ID to fetch
): T?

Example:

::: code-group

local Health = world:component() :: jecs.Entity<number>

local Entity = world:entity()
world:set(Entity, Health, 100)

print(world:get(Entity, Health))

-- Outputs:
-- 100

const Health = world.component<number>();

const Entity = world.entity();
world.set(Entity, Health, 100);

print(world.get(Entity, Health))

// Outputs:
// 100

:::

has

Returns whether an entity has a component (ID). Useful for checking if an entity has a tag or if you don't care of the data that is inside the component.

function World:has(
    entity: Entity, -- The entity
    id: Entity<T> -- The component ID to check
): boolean

Example:

::: code-group

local IsMoving = world:component()
local Ragdolled = world:entity() -- This is a tag, meaning it won't contain data
local Health = world:component() :: jecs.Entity<number>

local Entity = world:entity()
world:set(Entity, Health, 100)
world:add(Entity, Ragdolled)

print(world:has(Entity, Health))
print(world:has(Entity, IsMoving)

print(world:get(Entity, Ragdolled))
print(world:has(Entity, Ragdolled))

-- Outputs:
-- true
-- false
-- nil
-- true

const IsMoving = world.component();
const Ragdolled = world.entity(); -- This is a tag, meaning it won't contain data
const Health = world.component<number>();

const Entity = world.entity();
world.set(Entity, Health, 100);
world.add(Entity, Ragdolled);

print(world.has(Entity, Health));
print(world.has(Entity, IsMoving));

print(world.get(Entity, Ragdolled));
print(world.has(Entity, Ragdolled));

// Outputs:
// true
// false
// nil
// true

:::

add

Adds a component (ID) to the entity. Useful for adding a tag to an entity, as this adds the component to the entity without any additional values inside

function World:add(
    entity: Entity, -- The entity
    id: Entity<T> -- The component ID to add
): void

::: info This function is idempotent, meaning if the entity already has the id, this operation will have no side effects. :::

set

Adds or changes data in the entity's component.

function World:set(
    entity: Entity, -- The entity
    id: Entity<T>, -- The component ID to set
    data: T -- The data of the component's type
): void

Example:

::: code-group

local Health = world:component() :: jecs.Entity<number>

local Entity = world:entity()
world:set(Entity, Health, 100)

print(world:get(Entity, Health))

world:set(Entity, Health, 50)
print(world:get(Entity, Health))

-- Outputs:
-- 100
-- 50

const Health = world.component<number>();

const Entity = world.entity();
world.set(Entity, Health, 100);

print(world.get(Entity, Health)) 

world.set(Entity, Health, 50);
print(world.get(Entity, Health))

// Outputs:
// 100
// 50

:::

query

Creates a query with the given components (IDs). Entities that satisfies the conditions of the query will be returned and their corresponding data.

function World:query(
    ...: Entity -- The components to query with
): Query

Example:

::: code-group

-- Entity could also be a component if a component also meets the requirements, since they are also entities which you can add more components onto
for entity, position, velocity in world:query(Position, Velocity) do
	
end

// Roblox-TS allows to deconstruct tuples on the act like if they were arrays!
// Entity could also be a component if a component also meets the requirements, since they are also entities which you can add more components onto
for (const [entity, position, velocity] of world.query(Position, Velocity) {
    // Do something
}

:::

:::info Queries are uncached by default, this is generally very cheap unless you have high fragmentation from e.g. relationships.

:::

target

Get the target of a relationship. This will return a target (second element of a pair) of the entity for the specified relationship. The index allows for iterating through the targets, if a single entity has multiple targets for the same relationship. If the index is larger than the total number of instances the entity has for the relationship or if there is no pair with the specified relationship on the entity, the operation will return nil.

function World:target(
    entity: Entity, -- The entity
    relation: Entity, -- The relationship between the entity and the target
    nth: number, -- The index
): Entity? -- The target for the relationship at the specified index.

parent

Get parent (target of ChildOf relationship) for entity. If there is no ChildOf relationship pair, it will return nil.

function World:parent(
    child: Entity -- The child ID to find the parent of
): Entity? -- Returns the parent of the child

This operation is the same as calling:

world:target(entity, jecs.ChildOf, 0)

contains

Checks if an entity or component (id) exists in the world.

function World:contains(
    entity: Entity,
): boolean

Example:

::: code-group

local entity = world:entity()
print(world:contains(entity))
print(world:contains(1))
print(world:contains(2))

-- Outputs:
-- true
-- true
-- false

const entity = world.entity();
print(world.contains(entity));
print(world.contains(1));
print(world.contains(2));

// Outputs:
// true
// true
// false

:::

remove

Removes a component (ID) from an entity

function World:remove(
    entity: Entity,
	component: Entity<T>
): void

Example:

::: code-group

local IsMoving = world:component()

local entity = world:entity()
world:add(entity, IsMoving)

print(world:has(entity, IsMoving)) 

world:remove(entity, IsMoving)
print(world:has(entity, IsMoving))

-- Outputs:
-- true
-- false

const IsMoving = world.component();

const entity = world.entity();
world.add(entity, IsMoving);

print(world.has(entity, IsMoving));

world.remove(entity, IsMoving);
print(world.has(entity, IsMoving));

// Outputs:
// true
// false

:::

delete

Deletes an entity and all of its related components and relationships.

function World:delete(
    entity: Entity
): void

Example:

::: code-group

local entity = world:entity()
print(world:has(entity))

world:delete(entity)

print(world:has(entity))

-- Outputs:
-- true
-- false

const entity = world.entity();
print(world.has(entity));

world.delete(entity);

print(world.has(entity));

// Outputs:
// true
// false

:::

clear

Clears all of the components and relationships of the entity without deleting it.

function World:clear(
    entity: Entity
): void