watch deep

watch:{
  form: {
    handler(val){
      if (val.userId){
        this.userList.forEach(item => {
          if (val.userId === item.userId){
            this.form.nickName = item.nickName
          }
        });
      }

      if (val.fromId){
        this.userList.forEach(item => {
          if (val.fromId === item.userId){
            this.form.fromNickName = item.nickName
          }
        });
      }
    },
    deep: true
  }
},