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

Note: This feature is available in Web Workers.

Constructor

CustomEvent()
Creates a CustomEvent.

Properties

CustomEvent.detail Read only
Any data passed when initializing the event.

This interface inherits properties from its parent, Event:

Event.bubbles Read only
A Boolean indicating whether the event bubbles up through the DOM or not.
Event.cancelBubble
A non-standard alternative to Event.stopPropagation(). Setting its value to true before returning from an event handler prevents propagation of the event.
Event.cancelable Read only
A Boolean indicating whether the event is cancelable.
Event.currentTarget Read only
A reference to the currently registered target for the event. This is the object to which the event is currently slated to be sent to; it's possible this has been changed along the way through retargeting.
Event.deepPath 
An Array of DOM Nodes through which the event has bubbled.
Event.defaultPrevented Read only
Indicates whether or not event.preventDefault() has been called on the event.
Event.eventPhase Read only
Indicates which phase of the event flow is being processed.
Event.explicitOriginalTarget Read only
The explicit original target of the event (Mozilla-specific).
Event.originalTarget Read only
The original target of the event, before any retargetings (Mozilla-specific).
Event.returnValue
A non-standard alternative (from old versions of Microsoft Internet Explorer) to Event.preventDefault() and Event.defaultPrevented.
Event.scoped  Read only  
A Boolean indicating whether the given event bubbles. If this value is truedeepPath will only contain a target node.
Event.srcElement
A non-standard alias (from old versions of Microsoft Internet Explorer) for Event.target.
Event.target Read only
A reference to the target to which the event was originally dispatched.
Event.timeStamp Read only
The time at which the event was created, in milliseconds. By specification, this value is time since epoch, but in reality browsers' definitions vary; in addition, work is underway to change this to be a DOMHighResTimeStamp instead.
Event.type Read only
The name of the event (case-insensitive).
Event.isTrusted Read only
Indicates whether or not the event was initiated by the browser (after a user click for instance) or by a script (using an event creation method, like event.initEvent)

Methods

CustomEvent.initCustomEvent()

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

This interface inherits methods from its parent, Event:

Event.initEvent()
Initializes the value of an Event created. If the event has already being dispatched, this method does nothing.
Event.preventBubble() Obsolete since Gecko 24
Prevents the event from bubbling. Obsolete, use event.stopPropagation instead.
Event.preventCapture() Obsolete since Gecko 24
Obsolete, use event.stopPropagation instead.
Event.preventDefault()
Cancels the event (if it is cancelable).
Event.stopImmediatePropagation()
For this particular event, no other listener will be called. Neither those attached on the same element, nor those attached on elements which will be traversed later (in capture phase, for instance)
Event.stopPropagation()
Stops the propagation of events further along in the DOM.
Event.getPreventDefault()
Non-standard. Returns the value of Event.defaultPrevented. Use Event.defaultPrevented instead.

Specifications

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

Browser compatibility

        
Feature Chrome Edge Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support (Yes)(Yes) 6 9 11 5.1 (533.3)
CustomEvent() constructor 15? 11 No support 11.60 Nightly build (535.2)
Available in workers (Yes)? 48 (48) (Yes) (Yes) (Yes)
     
Feature Android Edge Firefox Mobile (Gecko) IE Phone Opera Mobile Safari Mobile
Basic support ?(Yes) ? ? ? ?
Available in workers (Yes)? 48.0 (48) (Yes) (Yes) (Yes)

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 Objects 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);
  doc.dispatchEvent(myEvent);
}

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