为什么Pusher没有取消订阅？

I have some code that creates a chat room, and in beforeDestroy method, i want to unsubscribe from the chat room channel. I use the following code to achieve this, however this doesnt work:

    beforeDestroy()
    {
        let roomId = this.app.$route.params.id;
        pusher.unsubscribe('presence-chat.'+roomId);
    },