await仅在异步函数中有效-node.js

Question

I'm using node and express to create server for my app. This is how my code looks like:

async function _prepareDetails(activityId, dealId) {

  var offerInfo;
  var details = [];


  client.connect(function(err) {
    assert.equal(null, err);
    console.log("Connected correctly to server");

    const db = client.db(dbName);
    const offers_collection = db.collection('collection_name');

    await offers_collection.aggregate([
      { "$match": { 'id': Id} },
    ]).toArray(function(err, docs) {
      assert.equal(err, null);
      console.log("Found the following records");
      details = docs;
    });
  })
  return details;
}

app.post('/getDetails',(request,response)=>{

  var Id = request.body.Id;
  var activityId = request.body.activityId;
  _prepareDetails(activityId,Id).then(xx => console.log(xx));
  response.send('xx'); 
})

While calling getDetails API I am getting

await is only valid in async function error (At line await offers_collection.aggregate)

I am also getting red underline while declaring async function . Node version I'm using is 11.x. I'm also using firebase API. What am I doing wrong here?

Answer 1

You are missing the async declaration on one of your functions. Here is the working code:

async function _prepareDetails(activityId, dealId) {

  var offerInfo;
  var details = [];


  client.connect(async function(err) {
    assert.equal(null, err);
    console.log("Connected correctly to server");

    const db = client.db(dbName);
    const offers_collection = db.collection('collection_name');

    await offers_collection.aggregate([
      { "$match": { 'id': Id} },
    ]).toArray(function(err, docs) {
      assert.equal(err, null);
      console.log("Found the following records");
      details = docs;
    });
  })
  return details;
}

app.post('/getDetails', async (request,response)=>{

  var Id = request.body.Id;
  var activityId = request.body.activityId;
  let xx = await _prepareDetails(activityId,Id);
  response.send('xx'); 
})

Await can only be used in an async function, because await is by definition asynchronous, and therefore must either use the callback or promise paradigm. By declaring a function as async, you are telling JavaScript to wrap your response in a promise. Your issue was on the following line:

  client.connect(function(err) {

This is where I added the async as mentioned before.

client.connect(async function(err) {

You will notice I made your route use async also, because you would've had an issue before. Notice the two lines in your original code:

  _prepareDetails(activityId,Id).then(xx => console.log(xx));
  response.send('xx'); 

Your response would send before you even made your database call because you are not wrapping the response.send within the .then. You could move the response.send into the .then, but if you are going to use async/await, I would use it all the way. So your new route would look like:

app.post('/getDetails', async (request,response)=>{

  var Id = request.body.Id;
  var activityId = request.body.activityId;
  let xx = await _prepareDetails(activityId,Id);
  response.send('xx'); 
})