The RTCDTMFToneChangeEvent interface represents events sent to indicate that DTMF tones have started or finished playing. This interface is used by the tonechange event.


In addition to the properties of Event, this interface offers the following:

RTCDTMFToneChangeEvent.tone Read only

A DOMString specifying the tone which has begun playing, or an empty string ("") if the previous tone has finished playing.



Returns a new RTCDTMFToneChangeEvent. It takes two parameters, the first being a DOMString representing the type of the event (always "tonechange"); the second a dictionary containing the initial state of the properties of the event.


Supports the methods defined in Event. There are no additional methods.


This snippet is derived loosely from the full, working example you'll find in When a tone finishes playing in Using DTMF with WebRTC. It appends each tone to a display box as it's played, and, once all tones have been sent, re-enabled a previously-disabled "Send" button, allowing the next DMTF string to be entered.

dtmfSender.addEventListener("change", function(event) {
  if (event.tone !== "") {
    dialStringBox.innerText += event.tone;
  } else {
    sendDTMFButton.disabled = false;
}, false);


WebRTC 1.0: Real-Time Communication Between Browsers (WebRTC 1.0)
# dom-rtcdtmftonechangeevent

Browser compatibility

BCD tables only load in the browser

See also