The CustomEvent interface represents events initialized by an application for any purpose.

Note: This feature is available in Web Workers



Creates a CustomEvent.


This interface inherits properties from its parent, Event.

CustomEvent.detail Read only

Any data passed when initializing the event.


This interface inherits methods from its parent, Event.


Initializes a CustomEvent object. If the event has already being dispatched, this method does nothing.


DOM Standard (DOM)
# interface-customevent

Browser compatibility

BCD tables only load in the browser

Firing from privileged code to non-privileged code

When firing a CustomEvent from privileged code (i.e. an extension) to non-privileged code (i.e. a webpage), security issues should be considered. Firefox and other Gecko applications restrict an object created in one context from being directly used for another, which will automatically prevent security holes, but these restrictions may also prevent your code from running as expected.

While creating a CustomEvent object, you must create the object from the same window. The detail attribute of your CustomEvent will be subjected to the same restrictions. String and Array values will be readable by the content without restrictions, but custom Object will not. While using a custom object, you will need to define the attributes of that object that are readable from the content script using Components.utils.cloneInto().

// doc is a reference to the content document
function dispatchCustomEvent(doc) {
  var eventDetail = Components.utils.cloneInto({foo: 'bar'}, doc.defaultView);
  var myEvent = doc.defaultView.CustomEvent("mytype", eventDetail);

But one needs to keep in mind that exposing a function will allow the content script to run it with chrome privileges, which can open a security vulnerability.

See also