I am receive the error: TypeError: this.room.state.players.onAdd is not a function

My client side create():

	async create() {
		console.log("Joining room...");

		try {
			this.room = await this.client.joinOrCreate("my_room");
			console.log("Joined Room");
		} catch (e) {
			console.error(e);
		}
		this.room.state.players.onAdd((player: any, sessionId: any) => {
			//
			// A player has joined!
			//
			console.log("A player has joined! Their unique session id is", sessionId);
		});
	}

My server side RoomState:

// MyRoomState.ts
import { MapSchema, Schema, type } from "@colyseus/schema";

export class Player extends Schema {
  @type("number") x: number;
  @type("number") y: number;
}

export class MyRoomState extends Schema {
  @type({ map: Player }) players = new MapSchema<Player>();
}

And lastly (the relevant parts of) OnJoin:

  onJoin(client: Client, options: any) {
    console.log(client.sessionId, "joined");
    const mapWidth = 200;
    const mapHeight = 300;

    // create Player instance
    const player = new Player();

    // place Player at a random position
    player.x = (Math.random() * mapWidth);
    player.y = (Math.random() * mapHeight);

    // place player in the map of players by its sessionId
    // (client.sessionId is unique per connection!)
    this.state.players.set(client.sessionId, player);
  }

Any guidance appreciated !

Currently 0.15 is on preview, so you can fix this by installing 0.15@preview on the client-side:

npm install colyseus.js@preview --save

Hope this helps, cheers!

Updating both server and client to 0.15 has done the job.

Thankyou for your time