How to use the Promise.all() function

Question

I am creating a university project to display events that are happening in Leeds. I've almost completed this page which I am doing by using an EventbriteAPI. However, at the moment my page does not load until it has figured out all the event's venue names which takes quite a few seconds.

I believe I need to use a Promise.all() function to achieve this, but I'm struggling to understand how to implement it as I'm fairly new to this.

eventbrite.js

class EventBrite {
    constructor() {
        this.auth_token = 'Example';
        this.orderby = 'date';
        this.city = 'Leeds';
    }

    //Load Leeds events from API
    async loadAPI() {
        const initalEvents = await fetch(`https://www.eventbriteapi.com/v3/events/search/?sort_by=${this.orderby}&location.address=${this.city}&token=${this.auth_token}`);

        const events = await initalEvents.json();

        return {
            events
        }
    }

    async loadVenue(venueID) {
        const initalVenue = await fetch(`https://www.eventbriteapi.com/v3/venues/${venueID}/?token=${this.auth_token}`);

        const venue = await initalVenue.json();

        return venue;
    }
}

app.js

eventbrite.loadAPI()
    .then(async events => {
        //Check for events
        const eventsList = events.events.events;

        //Print venue IDs
        for(let i = 0, l = eventsList.length; i < l; i++) {
            const venueID = eventsList[i].venue_id;

            let venue = await eventbrite.loadVenue(venueID);
            eventsList[i].venue = venue.name
        }
        ui.displayEvents(eventsList);
    }
)

ui.js

class UI {
    constructor() {
        this.init();
    }
    init() {
        this.printCategories();

        this.result = document.getElementById('result');
    }

    //Display events
    displayEvents(events) {   
        //Build template
        let HTMLTemplate = '';
        events.forEach(eventInfo => {
            HTMLTemplate += `
                <div class="row">
                    <div class="column">
                        <p class="event">${eventInfo.name.text}</p>
                        <p class="event">${eventInfo.venue}</p>
                        <p class="event">${eventInfo.start.local}</p>
                    </div>
                </div>
            `;
        });
        this.result.innerHTML = HTMLTemplate;
    }
}

Answer 1

One Problem is, that you make all these calls in series, wich means, that the time to complete them is adding up.

Better run them in paralell:

eventbrite.loadAPI()
    .then(async events => {
        let promises = events.events.events.map(async (eventInfo) => {
            let venue = await eventbrite.loadVenue(eventInfo.venue_id);
            eventInfo.venue = venue.name;
            return eventInfo;
        });

        const eventsList = await Promise.all(promises);

        ui.displayEvents(eventsList);
    });

If the responses are stil returning slow AND with a big difference between the first and the last one, you could render the intermediate results:

eventbrite.loadAPI()
    .then(events => {
        const eventsList = events.events.events;

        eventsList.forEach(async (eventInfo) => {
            let venue = await eventbrite.loadVenue(eventInfo.venue_id);
            eventInfo.venue = venue.name;

            ui.displayEvents(eventsList.filter(item => item.venue));
        });
    });