system/unload

We are planning to deprecate the use by Firefox add-ons of the techniques described in this document.

Don't use these techniques to develop new add-ons. Use WebExtensions instead.

If you maintain an add-on which uses the techniques described here, consider migrating it to use WebExtensions instead.

Add-ons developed using these techniques might not work with multiprocess Firefox (e10s), which is already the default in Firefox Nightly and Firefox Developer Edition, and will soon be the default in Beta and Release versions of Firefox. We have documentation on making your add-ons multiprocess-compatible, but it will be more future-proof for you to migrate to WebExtensions.

A wiki page containing resources, migration paths, office hours, and more, is available to help developers transition to the new technologies.

Experimental

Register callbacks that are called when a module is unloaded.

Globals

Functions

ensure(object, name)

Calling ensure() on an object does two things:

  1. It replaces a destructor method with a wrapper method that will never call the destructor more than once.
  2. It ensures that this wrapper method is called when the object's module is unloaded.

Therefore, when you register an object with ensure(), you can call its destructor method yourself, you can let it happen for you, or you can do both.

The destructor will be called with a single argument describing the reason for the unload; see when(). If object does not have the expected destructor method, then an exception is thrown when ensure() is called.

Parameters

object : object
An object that defines a destructor method.

name : string
Optional name of the destructor method. Default is unload.

when(callback)

Registers a function to be called when the module is unloaded.

Parameters

callback : function
A function that will be called when the module is unloaded. It is called with a single argument, one of the following strings describing the reason for unload: "uninstall", "disable", "shutdown", "upgrade", or "downgrade". If a reason could not be determined, undefined will be passed instead. Note that if an add-on is unloaded with reason "disable", it will not be notified about "uninstall" while it is disabled. See bug 571049.

Document Tags and Contributors

 Contributors to this page: wbamberg
 Last updated by: wbamberg,