JavaScript 使用 parseInt 解析数字并求和

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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>用parseInt解析数字，并求和</title>
<style> 
body{font:12px/1.5 arial;text-align:center;}
.f-text{width:50px;border:1px solid #ccc;background:#f0f0f0;font-family:inherit;padding:3px;}
span{color:green;padding-right:10px;font-weight:700;}
strong{padding:0 10px;}
</style>
<script type="text/javascript"> 
window.onload = function ()
{
 var aInput = document.getElementsByTagName("input");
 var aSpan = document.getElementsByTagName("span")[0];
 var i = 0;
 for (i = 0; i < aInput.length - 1; i++)
 {
  aInput[i].onkeyup = function ()
  {
   this.value = this.value.replace(/[^\d]/,"")
  } 
 }
 aInput[2].onclick = function ()
 {
  (aInput[0].value == "" || aInput[1].value == "") ?
  alert("请输入数字！") :
  aSpan.innerHTML = parseInt(aInput[0].value) + parseInt(aInput[1].value);
 }
};
</script>
</head>
<body>
<input type="text" class="f-text" /><strong>+</strong><input type="text" class="f-text" /><strong>=</strong><span>?</span><input type="button" value="求和" />
</body>
</html>