我想等待三個 HTTP 請求完成，然后再調用另一個函數來處理三個 HTTP 請求返回的數據。我嘗試循環房間數（相當于所需的 HTTP 請求數），然后將設備推入數組。在將設備數組傳遞給下一個要處理的函數之前，我需要完成所有三個 HTTP 請求。getDeviceListByRoom(rooms_id_array: string[]) {    console.log('The rooms_id_array is: ', rooms_id_array);    this.room_device_map = new Map;    let count = 0;    for (const id of rooms_id_array) {      const devicesByRoom = this.Services.getDeviceByRoom(id);      devicesByRoom.subscribe((res: any) => {        if (res.code === 200) {          // this statement will map the list of devices to the room.          this.room_device_map.set(id, res.data);          // this statement will just push the list of devices from different room into one array.          this.all_devices_list.push(res.data);          console.log('count is: ', count++);        }      }, err => {        console.error('ERROR', err);      });      console.log('In all_devices_list is: ', this.all_devices_list);    }    console.log('Lalalalal');  }The code above will return 'Lalalala' first followed by the console print out of the count variable. Understandably, the for...of function is non blocking...?