---
title: "Events in the _st module"
slug: "events-in-the-st-module"
description: "Use the _st.event module to publish and subscribe to custom events in the Data Activation tag system, enhancing your tag setup's interactivity."
updated: 2026-07-13T06:10:34Z
published: 2026-07-13T06:10:34Z
canonical: "docs.supermetrics.com/events-in-the-st-module"
---

> ## Documentation Index
> Fetch the complete documentation index at: https://docs.supermetrics.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Events in the _st module

The `_st.event` module provides a simple event bus within the Data Activation tag system. Use it to publish custom events from one part of your tag setup and subscribe to them from another, without those parts needing to call each other directly.

## Methods overview

| Method | Description |
| --- | --- |
| `_st.event.publish(category, eventName, data)` | Clarifies the trailing slash behavior |
| `_st.event.subscribe(category, eventName, callback)` | Subscribes to an event. |

## Method details

### _st.event.publish(category, eventName, data)

Data Activation runs the callback for every subscription where the category matches or is a parent of the published category, and the event name matches exactly (or uses a wildcard).

**Parameters:**

- **category** (string): The event category. Use a selector delimited by `/`, for example `checkout/cart`.
- **eventName** (string): The name of the event. Must match exactly for a subscription to trigger.
- **data** (any): The data to pass to the subscriber's callback function.

**Requires:** `_st.event.subscribe`

**Example:**

```javascript
_st.event.publish('checkout/cart', 'itemAdded', { productId: '1630' });
```

### _st.event.subscribe(category, eventName, callback)

Subscribes to an event. When a matching event is published, Data Activation runs the callback function with the event's category, event name, and data.

**Parameters:**

- **category** (string): The event category to subscribe to. Use a selector delimited by `/`.
- **eventName** (string): The name of the event to subscribe to. Pass an empty string (`""`) to listen to all events published under the specified category.
- **callback** (function): The function to run when a matching event is published. Receives `category`, `eventName`, and `data` as parameters. Note: The category string passed to your callback will always include a trailing slash (such as `checkout/cart/`), even if it was published without one.

**Requires:** `_st.event.publish`

**Example:**

```javascript
// Exact event match
_st.event.subscribe('checkout', 'itemAdded', function(category, eventName, data) {
  // Receives: 'checkout/cart/', 'itemAdded', { productId: '1630' }
});

// Wildcard match (listens to all events under 'checkout')
_st.event.subscribe('checkout', '', function(category, eventName, data) {
  // Handles 'itemAdded', 'itemRemoved', 'paymentProcessed', etc.
});
```