Typescript ECS System

ecsSystem.ts

export type ComponentFn<T extends EcsComponent = EcsComponent> = new (
    ...args: any[]
) => T;

export type QueryData<T extends QueryObject = QueryObject> = {
    [P in keyof T]: InstanceType<T[P]>[];
};

export interface QueryObject<T extends ComponentFn = ComponentFn> {
    [componentName: string]: T;
}

type UpdateFunction<T extends QueryObject> = (
    components: QueryData<T>,
    gameTime: number,
) => void;

abstract class EcsComponent {}

export class EcsSystem<T extends QueryObject = QueryObject> {
    private onUpdate: UpdateFunction<T> | null = null;

    constructor(public query: Readonly<T>) {}

    runUpdate(components: QueryData<T>, gameTime: number) {
        if (this.onUpdate) {
            this.onUpdate(components, gameTime);
        }
    }

    withUpdate(updateFunction: UpdateFunction<T>): void {
        this.onUpdate = updateFunction;
    }
}

class CounterComponent extends EcsComponent {
    currentValue: number = 0;
}

const counterSystem = new EcsSystem({
    counter: CounterComponent,
});

counterSystem.withUpdate(({counter}) => {
    counter[0].currentValue += 42;
    console.log("Amount during update", counter[0].currentValue);
});