Correct way of returning data from function in NodeJS

Question

I'm new to Node so I'm struggling with getting the data from one function to another:

//dhtController.js
const dhtSensor = require('node-dht-sensor').promises;

exports.currentTemperature = async () => {
  const rawTemp = await dhtSensor.read(22, 4); // { temperature: 24, humidity: 60 }

  return rawTemp;
};




//dataController.js
const dhtController = require('./dhtController');

...
exports.getAllReadings = (req, res, next) => {
  const currentTemp = dhtController.currentTemperature(); // undefined

  res.status(200).json({
    status: 'success',
    currentTemp, // undefined
  });
};
...

I tried using async/await in dataController as well - no luck. Old callback-way works, however I rather keep things consistent and use async/await.

Can somebody help me out here? What am I missing? My guess is that in my dataController the results are not in the event loop yet. However 'awaiting' them did not help.

UPD:

Guys, thanks, I tried this from the very beginning:

exports.getAllReadings = async (req, res, next) => {
  const currentTemp = await dhtController.currentTemperature();

  console.log(JSON.stringify({ currentTemp: new Promise(() => {}) }));
  //{"currentTemp":{}}    

  res.status(200).json({
    status: 'success',
    message: 'Here we will have all sensors object',
    currentTemp, // empty
  });
};

Postman result:

{
    "status": "success",
    "message": "Here we will have all sensors object"
}

You need to add async keyword in getAllReadings and then use await before dhtController.currentTemperature() — Sebastian Kaczmarek
– Sebastian Kaczmarek, Commented Oct 15, 2019 at 15:07
Also, currentTemp is not undefined, it is an instance of Promise. If you JSON.stringify({ currentTemp: new Promise(() => {}) }) you get "{\"currentTemp\":{}}", not "{}", so I'm not sure what leads you to think currentTemp is undefined — Patrick Roberts
– Patrick Roberts, Commented Oct 15, 2019 at 15:09
Tried that earlier: exports.getAllReadings = async (req, res, next) => { const currentTemp = await dhtController.currentTemperature(); returns 'undefined' — falken
– falken, Commented Oct 15, 2019 at 15:11
That's not even possible. async functions always return promises, no exceptions. Please produce a minimal reproducible example because I'm certain either you're mistaken, or your example code is not representative of the situation. — Patrick Roberts
– Patrick Roberts, Commented Oct 15, 2019 at 15:14
Is dhtSensor = require('node-dht-sensor') or dhtSensor = require('node-dht-sensor').promises? If it's the former, that's your mistake. — Patrick Roberts
– Patrick Roberts, Commented Oct 15, 2019 at 15:19

Kevin.a · Accepted Answer · 2019-10-15 15:10:05Z

3

Since the function you're calling uses an await, you need to make the function you're calling it in async. Which makes sense since you're waiting for a result.

exports.getAllReadings = async (req, res, next) => {
  const currentTemp = await dhtController.currentTemperature(); 

  res.status(200).json({
    status: 'success',
    currentTemp, // undefined
  });
};

answered Oct 15, 2019 at 15:10

Kevin.a

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1 Comment

Praveen Kumar Purushothaman Over a year ago

Dude, 10 seconds! 😅

Praveen Kumar Purushothaman · Accepted Answer · 2019-10-15 15:10:17Z

3

Using async and await you can make it work:

exports.getAllReadings = async (req, res, next) => {
  const currentTemp = await dhtController.currentTemperature(); // undefined

  res.status(200).json({
    status: 'success',
    currentTemp, // will be defined
  });
};

answered Oct 15, 2019 at 15:10

Praveen Kumar Purushothaman

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