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


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.


Specification Status Comment
The definition of 'CustomEvent' in that specification.
Living Standard Initial definition.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support (Yes) 6 9 11 5.1 (533.3)
CustomEvent() constructor 15 11 Not supported 11.60 Nightly build (535.2)
Feature Android Firefox Mobile (Gecko) IE Phone Opera Mobile Safari Mobile
Basic support ? ? ? ? ?

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), you must take security into consideration. Firefox and other Gecko applications restrict an object created in one context from being directly used from another, which will generally automatically prevent security holes, but these restrictions may also prevent your code from running as expected.

When creating a CustomEvent object, you must create the object from the same window as you're going to fire against.

// doc is a reference to the content document
function dispatchCustomEvent(doc) {
  // This will not work. CustomEvent will be created from the chrome window and will not be seen by the content.
  // var myEvent = new CustomEvent("mytype");
  // Create CustomEvent from the content window
  var myEvent = doc.defaultView.CustomEvent("mytype");

The detail attribute of your CustomEvent will be subject to the same restrictions. String and Array values will be readable by the content without restrictions, but custom Objects will not. If using a custom Object, you will need to define the attributes of that object that are readable from the content script using __exposedProps__.

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

Note that exposing a function will allow the content script to run it with chrome privileges, which can open a security vulnerability.

See also

Document Tags and Contributors

Last updated by: Jeremie,