SpeechSynthesisUtterance: boundary event

The boundary event of the Web Speech API is fired when the spoken utterance reaches a word or sentence boundary.


Use the event name in methods like addEventListener(), or set an event handler property.

addEventListener("boundary", (event) => {});

onboundary = (event) => {};

Event type

Event properties

In addition to the properties listed below, properties from the parent interface, Event, are available.

charIndex Read only

Returns the index position of the character in the SpeechSynthesisUtterance.text that was being spoken when the event was triggered.

elapsedTime Read only

Returns the elapsed time in seconds after the SpeechSynthesisUtterance.text started being spoken that the event was triggered at.

name Read only

Returns the name associated with certain types of events occurring as the SpeechSynthesisUtterance.text is being spoken: the name of the SSML marker reached in the case of a mark event, or the type of boundary reached in the case of a boundary event.

utterance Read only

Returns the SpeechSynthesisUtterance instance that the event was triggered on.


You can use the boundary event in an addEventListener method:

utterThis.addEventListener("boundary", (event) => {
    `${event.name} boundary reached after ${event.elapsedTime} seconds.`,

Or use the onboundary event handler property:

utterThis.onboundary = (event) => {
    `${event.name} boundary reached after ${event.elapsedTime} seconds.`,


Web Speech API
# eventdef-speechsynthesisutterance-boundary
Web Speech API
# dom-speechsynthesisutterance-onboundary

Browser compatibility

BCD tables only load in the browser

See also