watcher.close() 关掉后，无法再监听。不知道如何再打开

requestId: "1618705516709_0.3624532906210909"

"watchid_1618705516705_0.3589298669638463"

【代码如下】

  imChat_get: function(useropenid){

    console.log("开始 imChat_get 方法")

    var that = this

    const db = wx.cloud.database()

    const _ = db.command

    db.collection('mailChat')

    .where({

      _openid: _.eq(app.globalData._openid).or(_.eq(useropenid)), 

    })

    .where({

      people: _.eq(useropenid).or(_.eq(app.globalData._openid))

    })

    .orderBy('createDate', 'asc')

    .limit(5)

    .watch({

      onChange: function(snapshot) {

        console.log('----------- snapshot为', snapshot)

        console.log('docChanges为', snapshot.docChanges)

        console.log("有聊天记录")

        that.setData({

          mailChatArray_new: snapshot.docChanges //最新消息

        })

        console.log('docs为', snapshot.docs)

        that.setData({

          mailChatArray: snapshot.docs //历史消息

        })

        console.log('is init data', snapshot.type === 'init')

        setTimeout(() => {

          await watcher.close()

        }, 300);

      },

      onError: function(err) {

        console.error('the watch closed because of error', err)

      }

    })

  },