An example of typing a proxy object to get/set properties in bitESC's components

component_proxy_type.ts

import {
  addComponent,
  addEntity,
  createWorld,
  defineComponent,
  defineQuery,
  type ComponentType,
  type IWorld,
  Types,
  type ISchema,
} from "bitecs";

// Schema
const Scalar = { v: Types.ui32 };
const Vector2 = { x: Types.ui32, y: Types.ui32 };

// Components
const Position = defineComponent(Vector2);
const Speed = defineComponent(Scalar);

// Queries
export const queryAll = defineQuery([]);

// Helpers
type SchemaProxy<S extends ISchema, V = number> = { [SK in keyof S]: V };
type GetSchema<T> = T extends ComponentType<infer U> ? U : never;
type ComponentMapProxy<C extends ComponentType<any>> = {
  [CK in keyof C]: SchemaProxy<GetSchema<C[CK]>>;
};

function createEntity<
  W extends IWorld,
  C extends Record<string, ComponentType<any>>
>(
  world: W,
  components: C
): { eid: ReturnType<typeof addEntity> } & ComponentMapProxy<C> {
  const eid = addEntity(world);
  const entity = { eid };
  for (const [name, component] of Object.entries(components)) {
    addComponent(world, component, eid);
    entity[name] = {};
    for (const property in component)
      if (!property.match(/^Symbol/))
        proxy[name] = {
          get [property]() {
            return component[property][eid];
          },
          set [property](v: number) {
            component[property][eid] = v;
          },
        };
  }
  return entity as any;
}

// Main
export const world = createWorld();
export const position = createEntity(world, { Position });
export const speed = createEntity(world, { Speed });
export const positionAndSpeed = createEntity(world, { Position, Speed });

position.Position.x = 1;
position.Position.y = 1;
speed.Speed.v = 10;
positionAndSpeed.Position.x = 1;
positionAndSpeed.Position.y = 1;
positionAndSpeed.Speed.v = 2;