CODEWITHSUNDEEP
node.jsexpressasync-awaitrenderrouter
Ando
Ando

Reputation: 325

How to get Express Node route to wait for function before rendering

I am trying to get a route to wait for an async function in another module to return before render runs, but no matter what I do, res.render always runs first. This is my current code, which actually just freezes and never loads:

router.get('/', function(req, res, next) {
  try {
    const cities = spreadsheet.getData()

  } catch(err) {
    console.log(err)
  }

  res.render('index', { cities: cities})
})

and the function it is waiting for is this:

exports.getData = function () {
  parsedData = [];
  accessSpreadsheet().then(function(data) {
    console.log(parsedData)
    return parsedData;
  });
};

const accessSpreadsheet = async() => {
  await doc.useServiceAccountAuth({
      client_email: process.env.GOOGLE_SERVICE_ACCOUNT_EMAIL,
      private_key: process.env.GOOGLE_PRIVATE_KEY,
    });
  const loadedDoc =  await doc.loadInfo();
  sheet = await doc.sheetsByIndex[0];
  const cells = await sheet.loadCells(allCells[cellsIndex]);
  const data = await parseData();
  const moreCells = await checkNextCells()

  return;
}

The render runs first, and the parsedData prints in the console. I also tried making the route async, and I tried res.render inside a callback. Is there any way to make this work?

Upvotes: 1

Views: 5518

Answers (2)

artfulbeest
artfulbeest

Reputation: 1483

In your router, spreadsheet.getData() being async, you need to handle it with async/wait, which will require your callback to be async.

 router.get('/', async function(req, res, next) {
  try {
    const cities = await spreadsheet.getData();

    res.render('index', { cities: cities}) // moved this to inside a try block

  } catch(err) {
    console.log(err)
    // you need to handle the exception here, return error message etc
  }

})

In getData, you need to return a promise that will be resolved when called in router.

exports.getData = async function () {
    let parsedData = [];  
   try {
     parsedData = await accessSpreadsheet();
    } catch (exc) {
      // handle exception here
    }
   return parsedData;
};

finally in accessSpreadsheet(), I do not see where you return the data parsed.

  const accessSpreadsheet = async() => {
  try{
  await doc.useServiceAccountAuth({
      client_email: process.env.GOOGLE_SERVICE_ACCOUNT_EMAIL,
      private_key: process.env.GOOGLE_PRIVATE_KEY,
    });
  let loadedDoc =  await doc.loadInfo();
  let sheet = await doc.sheetsByIndex[0];
  let cells = await sheet.loadCells(allCells[cellsIndex]); // cellsIndex is not defined
  let data = await parseData(); // are you to pass the sheet? do not know how parsedData() works
  let moreCells = await checkNextCells()

  return data; // assuming data is what is meant to be returned
} catch(exc) {
   // probably return null or re-raise exception
}
}

It is important to always use try/catch or then/catch when dealing with async code in NodeJS.

Hope it sheds some light!

Upvotes: 1

Rachit Anand
Rachit Anand

Reputation: 664

Since accessSpreadSheet is an async function, you either need to await or return the promise (as suggested by Patrick Roberts in the comment), in getData function, and similarly in the router.

Using async await you can update your code as below (not tested)

exports.getData = async function () {
  parsedData = [];
  parsedData = await accessSpreadSheet();
  return parsedData;
};

const accessSpreadsheet = async() => {
  await doc.useServiceAccountAuth({
      client_email: process.env.GOOGLE_SERVICE_ACCOUNT_EMAIL,
      private_key: process.env.GOOGLE_PRIVATE_KEY,
    });
  const loadedDoc =  await doc.loadInfo();
  sheet = await doc.sheetsByIndex[0];
  const cells = await sheet.loadCells(allCells[cellsIndex]);
  const data = await parseData();
  const moreCells = await checkNextCells()

  return;
}

And in the router

router.get('/', async function(req, res, next) {
  let cities;
  try {
    cities = await spreadsheet.getData()

  } catch(err) {
    console.log(err)
  }

  res.render('index', { cities: cities})
})

Upvotes: 2

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