js代码求详细介绍下

<script language="javascript" type="text/javascript">
	var code;
	function createCode() {
	code = "";
	var codeLength = 4; //验证码的长度
	var checkCode = document.getElementById("checkCode");
	var codeChars = new Array(0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
	'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z',
	'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'); //所有候选组成验证码的字符，当然也可以用中文的
	for (var i = 0; i < codeLength; i++)
	{
	var charNum = Math.floor(Math.random() * 52);
	code += codeChars[charNum];
	}
	if (checkCode)
	{
	checkCode.className = "code";
	checkCode.innerHTML = code;
	}
	}
	function validateCode()
	{
	var inputCode = document.getElementById("inputCode").value;
	if (inputCode.length <= 0)
	{
	alert("请输入验证码！");
	}
	else if (inputCode.toUpperCase() != code.toUpperCase())
	{
	alert("false！");
	createCode();
	}
	else
	{
	alert("ture！");
	}
	}
	</script>

	</head>
	<body onLoad="createCode()">
	<form id="form1" runat="server" onSubmit="validateCode()">
	<div>
	<table border="0" cellspacing="5" cellpadding="5" >
	<tr>
	<td></td><td> <div class="code" id="checkCode" onClick="createCode()" ></div></td>
	</tr>
	<tr>
	<td>验证码：</td><td><input style="float:left;" type="text" id="inputCode" /></td><td>请输入验证码</td>
	</tr>
	<tr><td></td><td><input id="Button1" onclick="validateCode();" type="button" value="确定" /></td><td></td>
	</tr>
	</table>
	</div>
	</form>
	</body>

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