Method on

packages/server/src/socket/__tests__/socket-gateway.test.ts:36–39

(event: string, handler: (...args: any[]) => void)

    this.id = id;
    this.namespace.addSocket(this);
  }

  on(event: string, handler: (...args: any[]) => void) {
    this.handlers.set(event, handler);
    return this;
  }