Components

Components are meant to be data bags and nothing more. All logic should be placed in (EntitySystems). So it is recommended to declare components like plain c-structs. Adding getters and setters is acceptable though.

Creating component classes

To define a new component, you only need to extend the Component class.

In the following example we define two components: PositionComponent and VelocityComponent.

class PositionComponent extends Component {
	x = 0;
	y = 0;
}
class VelocityComponent extends Component {
	x = 0;
	y = 0;
}

The collection of components an entity has will determine its behavior. Adding components to an entity is dead easy. However, mind that entities can not hold two components of the same class. So, when you add a component type twice, the second one will replace the first one.

Adding Components to an Entity

You can assign components easily using add:

entity.add(new PositionComponent());
entity.add(new VelocityComponent());

Alternatively, you can assemble entities based on blueprints using a data-driven approach.

Removing Components From an Entity

You can remove components from entities any time (this might be delayed).

entity.remove(PositionComponent); // remove just one specific component
entity.removeAll(); // remove all components

Getting an Entities Component

Retrieving components can be done as follows.

const position = entity.get(PositionComponent);
const velocity = entity.get(VelocityComponent);

entity.get() will return null if the component does not exist in the entity. You can use entity.has() to check if the entity has a component of the specified class.

You can also get an entity using entity.require(). If the component does not exist, an exception will be thrown. You should use entity.require() only if you know that the component exist. For example if you are using an iterating EntitySystem, which already covers the existence with its Family.

const position = entity.require(PositionComponent);

Getting All Components

You can get all components at once by doing this.

const components = entity.getAll();

You can iterate over them either with a for of loop:

for (const component of components) {
	...
}

But also using a classic loop:

for (let i = 0; i < components.length; ++i) {
	const component = components[i];
	...
}