text: window.onload = function () {
    function loadDoc() {
      var xhttp = new XMLHttpRequest();
      xhttp.onreadystatechange = function () {
        if (this.readyState == 4 && this.status == 200) {
          document.getElementById("zhengwen").innerHTML = xhttp.response;
        }
      };
      xhttp.open("GET", "html/denglu.html", true);
      xhttp.send();
    }
    document.getElementById("denglu").addEventListener("click", loadDoc);
  
  // document.getElementsByTagName("div a")
    function loadHtml() {
      var xhttp = new XMLHttpRequest();
      xhttp.onreadystatechange = function () {
        if (this.readyState == 4 && this.status == 200) {
          document.getElementById("ketihuan").innerHTML = xhttp.response;
        }
      };
      xhttp.open("GET", "html/htmlcss.html", true);
      xhttp.send();
    }
    document.getElementById("htmlcss").addEventListener("click", loadHtml);
  
  document.getElementById("web").addEventListener("click",function(){
    var xhttp = new XMLHttpRequest();
    xhttp.onreadystatechange = function () {
      if (this.readyState == 4 && this.status == 200) {
        document.getElementById("ketihuan").innerHTML = xhttp.response;
      }
    };
    xhttp.open("GET", "html/weblist.html", true);
    xhttp.send();
  })
  
  
  
  
  
  
  }
  