Last updated 1 month ago

Fast.js Documentation

Throughout the login/checkout flow, Fast.js dispatches events to the host page that can be used to watch for and perform certain actions with, such as sending relevant data to Google Analytics.

Event object

Today, all events have a name field that denotes the type of event that fired (e.g. “Checkout - Order Created”), and some events have a properties field that contains special data relevant to the event that fired. For example, “Checkout - Order Created” events have the order_id, order_items, and total fields inside of their properties map.

Event list

These are all of the events that are currently supported, when they are sent, and what extra properties they contain.

Event list will soon be available in our API reference docs. Please subscribe to our product updates mailing list to be notified when this content becomes available.

Sample event watching code

Events can be monitored by adding an event listener to the Fast object, like so:

var fast = new Fast();
fast.addEventListener("user_event", (event) => {
  console.log(`fast.js got a user_event of type:${}!`);

  // Handle events here

In the // Handle events here block, you can do whatever you need with the event that has fired.

Sending data to Google Analytics

This sample block will watch for Order Created events from Fast.js and send them to Google Analytics:

var fast = new Fast();
fast.addEventListener("user_event", (event) => {
  if ( === "Checkout - Order Created") {
    gtag('event', 'purchase', {
        'event_category': 'Fast Checkout',
        'event_label': 'Fast Checkout Label',
        'value': + '.' +,
        'event_callback': function(id) {
                setTimeout(function() {
                  window.location = "";   
                }, 1000);