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 | TouchEvent |
| 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. |
| Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
|---|---|---|---|---|---|
| Basic support | (Yes)[1] | 9.0 (9.0)[2] | (Yes)[3] | No support | (Yes)[1] |
| Feature | Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
|---|---|---|---|---|---|
| Basic support | ? | 9.0 (9.0)[2] | ? | ? | ? |
[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.
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https://developer.mozilla.org/en-US/docs/Web/Events/compositionstart