title: ECS Entities #

ECS Entities #

Once components have been created, they can be added to entities.

Creating Entities #

Entities are created with two parameters, both optional. The first is either a unique number ID, a function to generate UIDs, or null which uses the default UID generator.

The second parameter is an object containing the components to add to the entity, with the key being the component ID (eg "identity") and the values being the component data.

const entity = new Entity(null, {
	identity: {
		name: "Bob",
		description: "A nice guy",
	},
});

const entity = new Entity(12345, {
	identity: {
		name: "Alice",
		description: "A nice lady",
	},
});

Components can also be assigned to entities with the addComponent method, which adds a single component.

const entity = new Entity();

entity.addComponent("identity", {
	name: "Bob",
	description: "A nice guy",
});

And, if the need arises, components can be removed from an entity with the removeComponent method. Removing components both deletes the data in the component and might make certain systems not operate on that entity any more.

entity.removeComponent("position");

Entity Spawners #

There are some entities which have a specific purpose, such as planets, stars, or ships. These entities are always created with the same components, so it might be helpful to create a factory function to create them.

// This is not a realistic example, but it shows how to create a spawner
function planetSpawner({
	name,
	description,
	position,
	radius,
	mass,
	atmosphere,
}: {
	name: string;
	description: string;
	position: { x: number; y: number; z: number };
	radius: number;
	mass: number;
	atmosphere: boolean;
}) {
	return new Entity(null, {
		identity: {
			name,
			description,
		},
		position,
		isPlanet: {
			radius,
			mass,
			atmosphere,
		},
	});
}