The MediaRecorder.onstart event handler (part of the MediaRecorder API) handles the start event, allowing you to run code in response to media recording being started by a MediaRecorder. 
 The start event is thrown as a result of the MediaRecorder.start() method being invoked. At this point, the data starts being gathered into a Blob. 
MediaRecorder.onstart = function(event) { ... } MediaRecorder.addEventListener('start', function(event) { ... })
... record.onclick = function() { mediaRecorder.start(); console.log("recorder started"); } mediaRecorder.onstart = function() { // do something in response to // recording being started } ...
None.
| Specification | 
|---|
| MediaStream Recording  # dom-mediarecorder-onstart  | 
| Desktop | Mobile | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | |
onstart | 
49  | 
79  | 
25  | 
No  | 
36  | 
14  | 
49  | 
49  | 
25  | 
36  | 
14  | 
5.0  | 
Navigator.getUserMedia
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    https://developer.mozilla.org/en-US/docs/Web/API/MediaRecorder/onstart