/DOM Events


The compositionstart event is fired when the composition of a passage of text is prepared (similar to keydown for a keyboard input, but fires with special characters that require a sequence of keys and other inputs such as speech recognition or word suggestion on mobile).

Bubbles Yes
Cancelable Yes
Target objects Element
Interface CompositionEvent


Property Type Description
target Read only EventTarget Focused element processing the composition.
type Read only DOMString The type of event.
bubbles Read only boolean Does the event normally bubble?
cancelable Read only boolean Is it possible to cancel the event?
view Read only WindowProxy Document.defaultView (window of the document)
detail Read only long (float) 0.
data Read only DOMString (string) The original string being edited, otherwise the empty string.
locale Read only DOMString (string) The language code for the composition event, if available; otherwise, the empty string.

Browser compatibility

We're converting our compatibility data into a machine-readable JSON format. This compatibility table still uses the old format, because we haven't yet converted the data it contains. Find out how you can help!

Feature Chrome Edge Firefox (Gecko) Internet Explorer Opera Safari
Basic support (Yes)[1] (Yes) 9.0 (9.0)[2] (Yes)[3] No support (Yes)[1]
Feature Android Edge Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support (Yes) (Yes) 9.0 (9.0)[2] ? ? No support

[1] The data attribute value is wrong.

[2] The event was fired in versions of Gecko before 9.0, but didn't have the DOM Level 3 attributes and methods.

Gecko doesn't support the locale attribute for trusted events yet. However, web developers can set this value via initCompositionEvent() when creating untrusted events.

According to the DOM Level3 specification, compositionstart is cancelable; however, Gecko doesn't currently let you cancel them.

Gecko fires this event when IME starts composition, and some platforms don't have an API for canceling composition once it's begun. In addition, Gecko can't know whether a keyboard event will start composition or not until IME actually starts composition. Because of this, event.preventDefault() doesn't work on compositionstart events in Gecko.

Gecko's editors (for example, <input type="text">, <div contenteditable/>, and designMode) start composition after the bubble phase of compositionstart. So, by the time your compositionstart handler is called, no contents have not been modified.

[3] The data value is always empty.

© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.