SpeechSynthesisUtterance: boundary event

Limited availability

This feature is not Baseline because it does not work in some of the most widely-used browsers.

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

Syntax

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

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

onboundary = (event) => { }

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) => {
  console.log(
    `${event.name} boundary reached after ${event.elapsedTime} seconds.`,
  );
});

Or use the onboundary event handler property:

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

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

This page was last modified on ⁨May 2, 2025⁩ by MDN contributors.