The message event of the MediaKeySession interface fires when a message is generated by the content decryption module. 
 The message event of the MediaKeySession interface fires when a message is generated by the content decryption module. 
Use the event name in methods like addEventListener(), or set an event handler property.
js
addEventListener("message", (event) => {}); onmessage = (event) => {};
A MediaKeyMessageEvent. Inherits from Event.
MediaKeyMessageEvent.message Read only 
Returns an ArrayBuffer with a message from the content decryption module. Messages vary by key system.
MediaKeyMessageEvent.messageType Read only 
Indicates the type of message. May be one of license-request, license-renewal, license-release, or individualization-request.
| Desktop | Mobile | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | |
message_event | 
5542–55Theonmessage event handler property is not supported. | 
79 | 52 | No | 4229–42Theonmessage event handler property is not supported. | 
12.1 | 5543–55Theonmessage event handler property is not supported. | 
5542–55Theonmessage event handler property is not supported. | 
52 | 4229–42Theonmessage event handler property is not supported. | 
12.2 | 6.04.0–6.0Theonmessage event handler property is not supported. | 
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    https://developer.mozilla.org/en-US/docs/Web/API/MediaKeySession/message_event