Async map function call to API returning an Array of undefined

Question

I'm quite new to Promises in JavaScript. I'm attempting to call an API to get calendar events using calendar IDs in an array. I do this by calling the API in a map function and attempt to put the resulting object as an array. However the result is simply an array of undefined objects.

From my Googling, Promises.all() should run when an async method completes. Why then are the results undefined?

PS: I debugged and can see the calendarObj is getting loaded from the API call correctly, however results is still undefined.

async function getCalendarEvents(calendarList) {
    if (debug) {
        console.log("searching between " + this.query.timeMin + " and " + this.query.timeMax);
    }
    var calendars = [];
    // Loop through all calendars and extract events
    const results = calendarList.map(async (calendar, i) => {
        if (calendar.summary != "Holidays in United Kingdom") {
            this.client.events.list({
                calendarId: calendar.id,
                timeMin: this.query.timeMin,
                timeMax: this.query.timeMax,
                maxResults: this.query.maxResults,
                singleEvents: true,
                orderBy: 'startTime',
            }, (err, res) => {
                if (err) return console.log('The API returned an error: ' + err);

                const events = res.data.items;

                if (events.length) {
                    if (debug) // true
                        console.log("Loading " + events.length + " events for " + calendar.summary);

                    var calendarObj = {
                        name: calendar.summary,
                        id: calendar.id,
                        events: events
                    };
                    // calendars.push(calendarObj);
                    return calendarObj;
                } else {
                    if (debug)
                        console.log('No upcoming events found for ' + calendar.summary);
                }
            });
        }
    });

    Promise.all(results).then((completed) => console.log(completed)); // returns an array of undefined
}

Console Output:

Your `async` function neither returns a Promise nor does it use `await` — Pointy, Oct 03 '18 at 13:32
Your `async (calendar, i) => { … }` does not `return` anything, that's why you're getting `undefined`. And it doesn't `await` anything either. You need to promisify your `this.client.events.list(…)` function - don't use a callback! — Bergi, Oct 03 '18 at 13:32
`Promises.all() should run when an async method completes` - correction, `Promise.all` (not Promises.all) resolves when all the Promises passed in the argument resolve (note, they don't even have to be all or any promises) — Jaromanda X, Oct 03 '18 at 13:45

Async map function call to API returning an Array of undefined

0 Answers0