The MediaRecorder.onstartevent 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 onstart property of the SpeechRecognition interface represents an event handler that will run when the speech recognition service has begun listening to incoming audio with intent to recognize grammars associated with the current SpeechRecognition (when the start event fires.)
The onstart property of the SpeechSynthesisUtterance interface represents an event handler that will run when the utterance has begun to be spoken (when the start event fires.)