console.log(document.readyState);

//監聽，當readystate狀態改變就觸發(loading,interactive,complete)
document.onreadystatechange = function () {

  console.log(document.readyState); 

  if (document.readyState == "loading") {
    //這邊一定不會進來，因為網頁一開始狀態就是loading，沒有改變，也不會觸發onreadystatechange
    console.log('The document is still loading.');
  }
  if (document.readyState == "interactive") {
    console.log('The document has finished loading and the document has been parsed but sub-resources such as images, stylesheets and frames are still loading.');
  }
  if (document.readyState == "complete") {
      // document is ready. Do your stuff here
    console.log('The document and all sub-resources have finished loading. The state indicates that the load event is about to fire.');
  }
}