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

Event RTCDTMFToneChangeEvent

Instance properties

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

RTCDTMFToneChangeEvent.tone Read only

A string 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 string representing the type of the event (always "tonechange"); the second a dictionary containing the initial state of the properties of the event.

Instance methods

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 the section on When a tone finishes playing. 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.

  (event) => {
    if (event.tone !== "") {
      dialStringBox.innerText += event.tone;
    } else {
      sendDTMFButton.disabled = false;


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

Browser compatibility

BCD tables only load in the browser

See also