I'm trying to make questionList a global variable so both router.post can use it because questionList use aggregate to take 10 random objects from a database, but it keeps having this error:

(node:17008) UnhandledPromiseRejectionWarning: TypeError: questionList is not iterable

const mongodb = require('mongodb');
const express = require('express');
const router = express.Router();
const app = express();
app.use(express.urlencoded());
app.use(express.json());

var questionList = async function (req, res, next) {
  next();
  const questionList = await req.database
    .collection('questions')
    .aggregate([{ $sample: { size: 10 } }])
    .toArray();
  return questionList;
};
app.use(questionList);

router.post('/attempts', async (req, res) => {
  let correctAnswers = {};
  for (const questions of questionList) {
    correctAnswers[questions._id] = questions.correctAnswer;
  }
  let attemptQuiz = {
    questions: questionList,
    correctAnswers,
    completed: false,
    startAt: new Date(),
  };

  let newAttemptQuiz = await req.database
    .collection('attempts')
    .insertOne(attemptQuiz);

  let renderAttemptsQuiz = await req.database
    .collection('attempts')
    .findOne({ _id: mongodb.ObjectID(`${newAttemptQuiz.insertedId}`) });

  const quesShow = renderAttemptsQuiz.questions;
  let objAll = [];
  let quest = {};
  for (const part of quesShow) {
    quest._id = part._id;
    quest.text = part.text;
    quest.answers = part.answers;
    objAll.push(quest);
  }

  let responseAttempt = {
    _id: renderAttemptsQuiz._id,
    questions: objAll,
    completed: false,
    startAt: new Date(),
  };
  res.status(200).json(responseAttempt);
});
router.post('/attempts/submit', async (req, res) => {
  let correctAnswers = {};
  for (const questions of questionList) {
    correctAnswers[questions._id] = questions.correctAnswer;
  }
  const clientAnswers = req.body;
  const count = 0;

  for (const ques of questionList) {
    if (correctAnswers[ques._id] == clientAnswers[ques._id]) {
      count  ;
    }
  }
  res.json({ score: count });
});
module.exports = router;

Please help me fix this!! Thanks very much

CodePudding user response：

You will need to cache your response in another variable.

let sample = []

var questionList = async function (req, res, next) {
  sample = await req.database
    .collection('questions')
    .aggregate([{ $sample: { size: 10 } }])
    .toArray()
  next()
};

for (const ques of sample) {
    if (correctAnswers[ques._id] == clientAnswers[ques._id]) {
      count  ;
    }
  }

Уou can also stash it in the request object.

var questionList = async function (req, res, next) {
  req._sample = await req.database
    .collection('questions')
    .aggregate([{ $sample: { size: 10 } }])
    .toArray()
  next()
};

for (const ques of req._sample) {
    if (correctAnswers[ques._id] == clientAnswers[ques._id]) {
      count  ;
    }
  }

Also, install your middleware on the router.

router.use(questionList);
// app.use(questionList);