第一次写js代码，求助

<head>

 <title>--!</title>

 <script type="text/javascript">

 /*

 *当textarea获得焦点，显示当前输入字数

 *当textarea失去焦点，隐藏

 */





 //获得焦点，显示

 function show_count(){

  var mydiv = document.getElementById("d");

  var max = 90;

  var count = document.getElementById("area1").value.length;

  if(mydiv.value ==""||mydiv.value ==undefined)

   mydiv.innerHtml =count +"/" + max;

  mydiv.style.display = "block";

 }



 //失去焦点，隐藏

 function hidden_count(){

  document.getElementById("d").style.display = "none";

 }



 //textarea域改变，改变div文本

 function word_count(){

  var mydiv = document.getElementById("d");

  var max = 90;

  var count = document.getElementById("area1").value.length;

  if(count<max)

   mydiv.innerHtml = count +"/" + max;

  else

   document.getElementsByTagName("textarea")[0].value = document.getElementsByTagName("textarea")[0].value.substr(0,max);

 }



 function load(){  var text = document.getElementsByTagName("textarea")[0];

  //请空

  text.value = "";

  text.focus();

 }

 </script>

 <style type="text/css">

 #d{

  display: none;

  position: absolute;

  width: 50px;

  height: 14px;

  color: black;

  background: yellow;

 }

 </style>

</head>

<body>

 <form>

  <textarea onfocus="show_count()" onblur="hidden_count()" 

  onload="load()" 

   onpropertychange="word_count()" cols="60" rows="8" id="area1">123</textarea>

  <div id="d">mxl</div>

 </form>

</body>

</html>