Website Builder > Event Handlers

Event Handlers

Learn how to react to Website Builder page lifecycle events using the event handler pattern.

WHAT YOU'LL LEARN

What are event handlers and when should you use them?
How do “Before” and “After” handlers differ?
How to implement a real-world event handler using the class-based pattern?
How to register event handlers in your project?

Overview

Event handlers let you hook into Website Builder page lifecycle events — points in time immediately before or after an operation (create, update, delete, publish, etc.) completes. You implement a class, register it as an extension, and the system calls it automatically during that operation.

Use event handlers when you need to:

Validate or modify page data before it is written (e.g., enforce a slug format)
Trigger side effects after an operation (e.g., notify an external system after a page is published)
Audit or log changes to pages

Before vs. After Handlers

Every operation has two hook points:

Handler type	When it runs	Can block the operation?	Payload contains
`Before`	Before the write	Yes — throw an error to abort	`input` (raw data being written)
`After`	After the write	No — operation already completed	`page` (the fully persisted page)

Use Before handlers for validation and data transformation. Use After handlers for side effects like webhooks or cache invalidation.

Anatomy of an Event Handler

Every event handler follows the same structure:

extensions/website-builder/page/eventHandler/update/beforeUpdate.ts

Key points:

The class must implement the Interface type exported from the handler namespace.
The handle method receives an event object — access data via event.payload.
Before handlers receive input (what is being written); After handlers receive page (what was persisted).
Dependencies are injected via the constructor — you do not instantiate them yourself.
The file must use export default.

Example: Enforce a Slug Format

This Before handler runs before a page is created and throws if the slug does not match a required pattern.

extensions/website-builder/page/eventHandler/create/beforeCreate.ts

Example: Notify an External System on Publish

This After handler fires after a page is published and sends the page data to an external webhook.

extensions/website-builder/page/eventHandler/publish/afterPublish.ts

Registering Event Handlers

After creating your handler files, register them in webiny.config.tsx using Api.Extension:

webiny.config.tsx

Each handler file is a separate Api.Extension entry. The order of registration determines the execution order when multiple handlers listen to the same event.

If a Before handler throws an error, the operation is aborted and subsequent handlers for the same event are not called. Design your validation logic accordingly.

Available Events

See the reference pages for the full list of available handlers:

Page Event Handlers — create, update, delete, publish, unpublish, duplicate, move, and revision creation
Redirect Event Handlers — create, update, delete, and move