window.speechSynthesis.getVoices（）如何工作

Question

无法获得此方法的工作方式。我已经尝试过使用eventListener（DOMContentLoaded）和window.onload。我不明白的是这种方法在不同情况下的响应。

// 1)
console.log(window.speechSynthesis,window.speechSynthesis.getVoices()) //Obj, empty Array

// 2)
setTimeout(() => {
    console.log(window.speechSynthesis.getVoices()); //empty Array
}, 10 * 1000);

// 3)
const x = window.speechSynthesis;
setTimeout(() => {
  console.log(window.speechSynthesis.getVoices()); //Array of objects
}, 0);

// 4)
const x = window.speechSynthesis;
console.log(window.speechSynthesis.getVoices()); //empty Array

// 5)
const x = window.speechSynthesis;
for(let i =0;i<10000;i++){
    console.log(i)
}
console.log(window.speechSynthesis.getVoices()); //empty Array