Definition
Web Speech API defines SpeechSynthesisErrorCode
enum SpeechSynthesisErrorCode {
"canceled",
"interrupted",
"audio-busy",
"audio-hardware",
"network",
"synthesis-unavailable",
"synthesis-failed",
"language-unavailable",
"voice-unavailable",
"text-too-long",
"invalid-argument",
"not-allowed",
};