The default read-only property of the SpeechSynthesisVoice interface returns a boolean value indicating whether the voice is the default voice for the current app (true), or not (false.)
Note: For some devices, it might be the default voice for the voice's language. The spec is not very clear on which it should be, so some implementations may differ.
A boolean value.
for (const voice of voices) {
const option = document.createElement("option");
option.textContent = `${voice.name} (${voice.lang})`;
if (voice.default) {
option.textContent += " — DEFAULT";
}
option.setAttribute("data-lang", voice.lang);
option.setAttribute("data-name", voice.name);
voiceSelect.appendChild(option);
}