api.SpeechSynthesisUtterance.boundary_event - supported in desktop Chrome since ???

[lionel-rowe]

What type of issue is this?

Incorrect support data (example: BrowserX says "86" but support was added in "40")

What information was incorrect, unhelpful, or incomplete?

SpeechSynthesisUtterance's boundary event is listed as follows:

"chrome": {
  "version_added": "33",
  "partial_implementation": true,
  "notes": "The `boundary` event does not fire as expected. See [bug 40715888](https://crbug.com/40715888)."
},
"chrome_android": "mirror",

However, it seems to be fully supported in latest desktop Chrome. The linked bug only mentions Android Chrome, so possibly desktop has had full support since v33? Android Chrome support is still lacking, meanwhile.

I think the correct data should be something like "chrome": { "version_added": "33" }, "chrome_android": { "version_added": false }, but not sure how to go about testing ancient versions of Chrome.

What browsers does this problem apply to, if applicable?

Chromium (Chrome, Edge 79+, Opera, Samsung Internet)

What did you expect to see?

"chrome": { "version_added": ??? }, "chrome_android": { "version_added": false }

Did you test this? If so, how?

Repro here: https://codepen.io/lionel-rowe/pen/zxrgrZL

$play.addEventListener('click', () => {
  speechSynthesis.cancel()
  CSS.highlights.delete('speaking')

  const utterance = new SpeechSynthesisUtterance(text)
  utterance.addEventListener('boundary', (e) => {
    const node = $output.childNodes[0]
    const range = new Range()
    range.setStart(node, e.charIndex)
    range.setEnd(node, e.charIndex + e.charLength)

    CSS.highlights.set('speaking', new Highlight(range))
  })
  utterance.addEventListener('end', () => {
    CSS.highlights.delete('speaking')
  })

  speechSynthesis.speak(utterance)
})

Runs fine on current desktop Chrome; on android, the boundary events fail to fire (no highlighting).

Can you link to any release notes, bugs, pull requests, or MDN pages related to this?

No response

Do you have anything more you want to share?

No response

MDN URL

https://developer.mozilla.org/en-US/docs/Web/API/SpeechSynthesisUtterance/boundary_event

MDN metadata

MDN page report details

• Query: api.SpeechSynthesisUtterance.boundary_event
• Report started: 2025-11-09T07:30:23.699Z