The length read-only property of the SpeechRecognitionResult interface returns the length of the "array" — the number of SpeechRecognitionAlternative objects contained in the result (also referred to as "n-best alternatives".)
The number of alternatives contained in the result depends on what the SpeechRecognition.maxAlternatives property was set to when the speech recognition was first initiated.
A number.
This code is excerpted from our Speech color changer example.
recognition.onresult = (event) => {
const color = event.results[0][0].transcript;
diagnostic.textContent = `Result received: ${color}.`;
bg.style.backgroundColor = color;
console.log(event.results[0].length);
};