頁面DOM-資源加載的相關標識

function func() {
  console.log('I am a callback);
}

window.onload = func
window.addEventListener('load', fun) => 至關於jquery中的ready事件
window.addEventListener('DOMContentLoaded', fun)
document.readyState === 'complete' | 
document.onreadystatechange = func

參考連接

readystatechange

load

onload

DOMContentLoaded

readyState