application_manager-7.js

  constructor(socket, remotePlayer, size, InputManager, Actuator, StorageManager) {
    ...

    // Add these two lines
    this.remotePlayer = remotePlayer;
    this.socket = socket;

    // Add this new if statement
    if (this.remotePlayer) {
      this.socket.on('move', this.handleRemoteMove.bind(this));
    }

    this.setup();
  }