Cannot read property 'forEach' of undefined with API

Question

I want to request all classes then all assignments of those classes from google classroom. For the class listing part, I used google's example code, for the assignment listing I used my own. The code runs and does what it is expected to do, lists the assignments, however it outputs

Execute error TypeError: Cannot read property 'forEach' of undefined at /home/daniel/nodegui-starter/src/index-nogui.ts:106:16 at processTicksAndRejections (internal/process/task_queues.js:97:5)

also. I have pasted the contents of the file below. as far as I understand it says that courseWork is undefined, but I define it just above? Can anyone help me?

const fs = require('fs');
const readline = require('readline');
const {google} = require('googleapis');

// If modifying these scopes, delete token.json.
const SCOPES = ['https://www.googleapis.com/auth/classroom.courses.readonly', 'https://www.googleapis.com/auth/classroom.coursework.me'];
// The file token.json stores the user's access and refresh tokens, and is
// created automatically when the authorization flow completes for the first
// time.
const TOKEN_PATH = 'token.json';

// Load client secrets from a local file.
fs.readFile('credentials.json', (err, content) => {
  if (err) return console.log('Error loading client secret file:', err);
  // Authorize a client with credentials, then call the Google Classroom API.
  // authorize(JSON.parse(coExecute error TypeError: Cannot read property 'forEach' of undefined
    at /home/daniel/nodegui-starter/src/index-nogui.ts:106:16
    at processTicksAndRejections (internal/process/task_queues.js:97:5)ntent), listCourses);
  authorize(JSON.parse(content), listCourses);
});

/**
 * Create an OAuth2 client with the given credentials, and then execute the
 * given callback function.
 * @param {Object} credentials The authorization client credentials.
 * @param {function} callback The callback to call with the authorized client.
 */
function authorize(credentials, callback) {
  const {client_secret, client_id, redirect_uris} = credentials.installed;
  const oAuth2Client = new google.auth.OAuth2(
      client_id, client_secret, redirect_uris[0]);

  // Check if we have previously stored a token.
  fs.readFile(TOKEN_PATH, (err, token) => {
    if (err) return getNewToken(oAuth2Client, callback);
    oAuth2Client.setCredentials(JSON.parse(token));
    callback(oAuth2Client);
  });
}

/**
 * Get and store new token after prompting for user authorization, and then
 * execute the given callback with the authorized OAuth2 client.
 * @param {google.auth.OAuth2} oAuth2Client The OAuth2 client to get token for.
 * @param {getEventsCallback} callback The callback for the authorized client.
 */
function getNewToken(oAuth2Client, callback) {
  const authUrl = oAuth2Client.generateAuthUrl({
    access_type: 'offline',
    scope: SCOPES,
  });
  console.log('Authorize this app by visiting this url:', authUrl);
  const rl = readline.createInterface({
    input: process.stdin,
    output: process.stdout,
  });
  rl.question('Enter the code from that page here: ', (code) => {
    rl.close();
    oAuth2Client.getToken(code, (err, token) => {
      if (err) return console.error('Error retrieving access token', err);
      oAuth2Client.setCredentials(token);
      // Store the token to disk for later program executions
      fs.writeFile(TOKEN_PATH, JSON.stringify(token), (err) => {
        if (err) return console.error(err);
        console.log('Token stored to', TOKEN_PATH);
      });
      callback(oAuth2Client);
    });
  });
}

/*function listAssignments(auth, courseId) {
  try {
  const classroom = google.classroom({version: 'v1', auth});
  classroom.courses.courseWork.list({
     "courseId": courseId
 }, (err, res) => {
     if (err) return console.error('The API returned an error: ' + err);
     const courseWork = res.data.courseWork;
     res.data.courseWork.forEach((assignment) => {
       if(assignment.dueDate){
         console.log(`${assignment.title} (${assignment.alternateLink}) ${assignment.dueDate.year}. ${assignment.dueDate.month}. ${assignment.dueDate.day}`);

     }
   else {       
      console.log(`${assignment.title} (${assignment.alternateLink})`);

   }
   });

 });
  }
  catch(error){
 console.log("you have an error in your code and you better go and cry")
        }
}
 */

function listAssignments(auth, courseId) {
  const classroom = google.classroom({version: 'v1', auth});

  return classroom.courses.courseWork.list({
      "courseId": courseId
  })
  .then(function(response) {
    var courseWork = response.data.courseWork;
    courseWork.forEach(assignment => {
     if (assignment.dueDate) {
      console.log(`${assignment.title} (${assignment.alternateLink}) ${assignment.dueDate.year}. ${assignment.dueDate.month}. ${assignment.dueDate.day}`);

     } 
     else {
      console.log(`${assignment.title} (${assignment.alternateLink})`);

     }
    });
  })
  .catch(function(err) { 
      console.error("Execute error", err); 
  });
};
/**
 * Lists the first 10 courses the user has access to.
 *
 * @param {google.auth.OAuth2} auth An authorized OAuth2 client.
 */
function listCourses(auth) {
  const classroom = google.classroom({version: 'v1', auth});
  classroom.courses.list({
    pageSize: 100,
  }, (err, res) => {
    if (err) return console.error('The API returned an error: ' + err);
    const courses = res.data.courses;
    if (courses && courses.length) {
      courses.forEach((course) => {
        try {
        listAssignments(auth,course.id)}
        catch(error){
 console.log("you have an error in your code and you better go and cry")
        }
      });
    } else {
      console.log('No courses found.');
    }
  });
}

Answer 1

I found the solution. I had a class where I had no courseWork yet, so I had to add a check at the beginning to check if courseWork exists.