Handlers

Last updated: 8 Apr 2025

The handlers module lets you define reactions to events.

Handlers respond to Events and return zero, one, or many Effects.

There are some special types of handlers, like Protocols and CronTasks. These offer a differentiated interface for their particular use-cases. For example, CronTasks only ever respond to the CRON event, require a schedule to be specified, and expect the execute method to be implemented rather than compute.

All handlers inherit from BaseHandler, which means you always have access to event and configuration data with the following accessors:

• self.event
  • Information about the event including the event type
• self.context
  • Data included as the event payload
• self.target
  • Identifying information to help you reference the subject of the event
• self.secrets
  • Configuration key-value store for your plugin
  • Secrets have their keys defined in the CANVAS_MANIFEST.json and their values are set by the Canvas instance administrator after installing your plugin via the Canvas UI on your plugin’s configuration page
• self.environment
  • Information about the Canvas instance your plugin is being executed on, like the subdomain, which we refer to as the customer identifier.
  • Example: self.environment['CUSTOMER_IDENTIFIER']

Action Button

Add a button that executes your custom code when clicked.

Application

Launch an iframe when your icon is clicked in the app drawer.

Cron Task

Execute your code on a cron-like schedule.

Base Handler

Respond to events with your custom code.