<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
	</head>
	<body>
		<p>


输入验证码：

<input type="text" name="" id="inputCode" value="" placeholder="请输入输入验证码"/>
			<span id="tyzm"></span>
		</p>

		<p> 

			<input type="button" name="" id="checkCode" value="获取验证码"onclick="createCode(4); " />
		</p>
		<p> 

			<input type="button" name="" id="" value="确定"onclick="validateCode()" />
		</p>

		<script type="text/javascript">			//页面加载时，生成随机验证码
    window.onload=function(){
     createCode(4);    
    }    //生成验证码的方法
    function createCode(length) {
        var code = "";
        var codeLength = parseInt(length); //验证码的长度
        var checkCode = document.getElementById("checkCode");
        var checkCode = document.getElementById("inputCode");
        ////所有候选组成验证码的字符，当然也可以用中文的
        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'); 
        //循环组成验证码的字符串
        for (var i = 0; i < codeLength; i++)
        {
            //获取随机验证码下标
            var charNum = Math.floor(Math.random() * 62);
            //组合成指定字符验证码
            code += codeChars[charNum];
        }
        if (checkCode)
        {
            //为验证码区域添加样式名
            checkCode.className = "code";
            //将生成验证码赋值到显示区
            tyzm.innerHTML = code;
        }
    }

    //检查验证码是否正确
    function validateCode()
    {
        //获取显示区生成的验证码
        var tyzm = document.getElementById("tyzm").innerHTML;
        //获取输入的验证码
        var inputCode = document.getElementById("inputCode").value;
        //console.log(checkCode);
        //console.log(inputCode);
        if (inputCode.length <= 0)
        {
            alert("请输入验证码！");
        }
        else if (inputCode.toUpperCase() != tyzm.toUpperCase())
        {
            alert("验证码输入有误！");
            createCode(4);
        }
        else
        {
            alert("验证码正确！");
        }       
    }  
		</script>
	</body>
</html>