The localService read-only property of the SpeechSynthesisVoice interface returns a boolean value indicating whether the voice is supplied by a local speech synthesizer service (true), or a remote speech synthesizer service (false.)
This property is provided to allow differentiation in the case that some voice options are provided by a remote service; it is possible that remote voices might have extra latency, bandwidth or cost associated with them, so such distinction may be useful.
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";
}
console.log(voice.localService);
option.setAttribute("data-lang", voice.lang);
option.setAttribute("data-name", voice.name);
voiceSelect.appendChild(option);
}