RTCDTMFToneChangeEvent: tone property

The read-only property RTCDTMFToneChangeEvent.tone returns the DTMF character which has just begun to play, or an empty string (""). if all queued tones have finished playing (that is, RTCDTMFSender.toneBuffer is empty).


A string with the DTML character playing, or the empty string.


This example establishes a handler for the tonechange event which updates an element to display the currently playing tone in its content, or, if all tones have played, the string "<none>".

dtmfSender.ontonechange = (ev) => {
  let tone = ev.tone;
  if (tone === "") {
    tone = "&lt;none&gt;";

  document.getElementById("playingTone").innerText = tone;


WebRTC: Real-Time Communication in Browsers
# dom-rtcdtmftonechangeevent-tone

Browser compatibility

BCD tables only load in the browser

See also