我不知道如何应用异步/等待概念

Question

I have the function below:

    let updateDevicesStatus = async () => {
       getAllConnectedClients()
       let teste = getAllDevices()

       try {
          devicesDB = await teste
       } catch (e) {
          console.log('deu erro')
       }
       devicesDB.forEach( (currentDevice) => {
          connectedClients.forEach( (currentClient) => {
             if (arduinoNM.connected[currentClient].clientID == currentDevice.clientID) {
                devicesOnline.push(currentDevice)
             } else {
                devicesOffline.push(currentDevice)
             }
          })
       })
}

getAllDevices() retrieve some data on DB, therefore, it takes more time to execute.

Node.JS run all these calls asynchronously, what causes an exception, saying that devicesDB is undefined.

I tried to use async/await to make updateDevicesStatus() wait for getAllDevices() execution, but it's not happening...

What I'm doing wrong?

getAllDevices() is not declared with async. Should I do it?

EDIT:

getAllDevicesPromise() function:

function getAllDevicesPromise() {
            return new Promise((resolve,reject) => {
                resolve(getAllDevices())
            })
        }

getAllDevices() function:

function getAllDevices() {
            let rst
            let query = Arduino.where({})
            query.find( (err, results) => {
                if (err) return console.error('[ERR] Erro buscando todos os dispositivos do banco para WEB.')
                rst = results
            })
            return rst
        }

I'm testing these function as below:

let test = await getAllDevicesPromise()
console.log(test)

But it still returning undefined. There's something more that I need to do?

Answer 1

let teste = getAllDevices() ... devicesDB = await teste

^^ This will not work as you expect because you are calling getAllDevices, assigning the return value to teste, and then waiting for nothing.

It should just be:

let devicesDB = await getAllDevices();

Answer 2

you can either :

use async/await which is a Syntactic Sugar For Promises in Javascript , you'll need to promisify the getAllDevices() function to resolve with the result of the query, and then await for it in the async updateDevicesStatus

function getAllDevices() {
    return new Promise((resolve, reject) => {
        let rst;
        let query = Arduino.where({});
        query.find((err, results) => {
          if (err) reject('[ERR] Erro buscando todos os dispositivos do banco para WEB.');

          resolve(results);
       });
    });
}

let updateDevicesStatus = async () => {
  getAllConnectedClients();

  let devicesDB = await getAllDevices();

  devicesDB.forEach((currentDevice) => {
    connectedClients.forEach((currentClient) => {
      if (arduinoNM.connected[currentClient].clientID == currentDevice.clientID) {
        devicesOnline.push(currentDevice);
      } else {
        devicesOffline.push(currentDevice);
      }
    });
  });
}

or use a callback :

function getAllDevices(cb) {
  let rst;
  let query = Arduino.where({});
  query.find((err, results) => {
    if (err) cb('[ERR] Erro buscando todos os dispositivos do banco para WEB.');

    cb(null, results);
  })
}

let updateDevicesStatus = () => {
  getAllConnectedClients()

  getAllDevices((err, devicesDB) => {
    if(err) // do something with the error

    devicesDB.forEach((currentDevice) => {
    connectedClients.forEach((currentClient) => {
      if (arduinoNM.connected[currentClient].clientID == currentDevice.clientID) {
        devicesOnline.push(currentDevice);
      } else {
        devicesOffline.push(currentDevice);
      }
    });
  });
}