What are userTrack callbacks?

The userTrack callbacks or hooks are a way to tap into the client-side userTrack tracking functionality and listen to specific events. This is useful, for example, if you want to read or forward some userTrack tracking data to another service.

Available callbacks

  • UST.onLoaded
    • Called as soon as the ust.min.js finishes loading.
  • UST.onTrackingStarted
    • Called when all tracking checks passed, meaning that a new session will be created.
  • UST.onSessionCreated(clientID: number)
    • Called when the userTrack server create a new session for this client
    • clientID: The integer number ID of the session.
    • This is called only once per visit for each visitor.
  • UST.onPageViewCreated(clientID: number, clientPageID: number)
    • Called when a new page has loaded and the server responded with the pageview ID.
    • clientID: The integer ID of the session.
    • clientPageID: The integer ID of the pageview.
    • This callback is also called once immediately after onSessionCreated (first pageview).
  • UST.onDataSent(data: string[])
    • Called whenever tracking data (session recording/heatmap data) is sent to the server.
    • data: An array of data strings sent to the server. Each data string is in the format c=XXX where c is the data type and XXX is the data value. The data type can be:
  • UST.onTagAdded(tag: string)
    • Called when UST.addTag() was called and the server responded.
    • tag: The string that has just been added as a tag to the current user.
  • UST.onEventAdded(eventData: Event)
    • Added in version 3.5.0
    • Called when UST.addEvent() was called and the server responded.
    • eventData: The original eventData passed, also containing clientID and clientPageID
  • UST.onGDPRAccepted
    • Called when the user accepted the tracking consent pop-up.
  • UST.onGDPRDeclined
    • Called when the user declined the tracking consent pop-up.

Usage example

Make sure write the callbacks declarations after the tracking file is included.
// <head>
// After ust.min.js include snippet
// ...
// <script>
// Example: User will be recorded
UST.onTrackingStarted = function() {
console.log('Creating session...!');
// Example: New session has been created with an unique clientID
UST.onSessionCreated = function(clientID) {
console.log('New session created for client', clientID);
// Example: whenever a tag is added, add the same tag + current pageID
UST.onTagAdded = function(tag) {
if (tag === 'AddToCart' || tag === 'Converted') {
UST.addTag(tag + ';' + sessionStorage.clientPageID);
// <script>
// </head>
After the session has been created (onSessionCreated), you can always read the current userTrack clientID and clientPageID from sessionStorage:
sessionStorage.getItem('token') token - Another unique identifier per session (similar to clientID). This is useful as it's not incremental.


Positions string (compressed format):

// For example:

Recording string (compressed format)

// This is more complex, looking at the data send or in the ust_records
// Should give you some idea of the format
// Some event names and their shorthand character:
enum PlaybackEventType {
CLICK = 'c',
SCROLL = 's',
// For example