1 JS实现验证码倒计时效果

效果如下：

<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <script type="text/javascript" src="../static/js/jquery-1.9.1.min.js"></script>
    <script type="text/javascript">
        $(function () {
        var wait=30;
        function time(o){
            if (wait==0) {
                o.removeAttribute("disabled");
                o.innerHTML="输入验证码";
                o.style.backgroundColor="#fe9900";
                wait=30;
            }else{
                o.setAttribute("disabled", true);
                o.innerHTML=wait+"秒后重新获取";
                o.style.backgroundColor="#8f8b8b";
                wait--;
                setTimeout(function(){
                    time(o)
                },1000)
            }
        }
        $(".getCode").click(function(){
            time(this);
        });
            })
    </script>
</head>
<body>
<button class="getCode" style="width: 120px;height: 50px;background: #FE9900;color: white;border: none">获取验证码</button>
</body>
</html>

2 JS生成验证码

效果如下：

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    <title>JS生成验证码</title>
    <style type="text/css">
        .code {
            background-image: url(code.jpg);
            font-family: Arial;
            font-style: italic;
            color: Red;
            border: 0;
            padding: 2px 3px;
            letter-spacing: 3px;
            font-weight: bolder;
        }
        .unchanged {
            border: 0;
        }
    </style>
    <script language="javascript" type="text/javascript">
        var code; //在全局 定义验证码
        function createCode() {
            code = "";
            var codeLength = 4;//验证码的长度
            var checkCode = document.getElementById("checkCode");
            var selectChar = 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');//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 charIndex = Math.floor(Math.random() * 36);
                code += selectChar[charIndex];
            }
            //alert(code);
            if (checkCode) {
                checkCode.className = "code";
                checkCode.value = code;
            }
        }

        function validate() {
            var inputCode = document.getElementById("input1").value;
            if (inputCode.length <= 0) {
                alert("请输入验证码！");
            } else if (inputCode != code) {
                alert("验证码输入错误！");
                createCode();//刷新验证码
            } else {
                alert("^-^ OK");
            }
        }
    </script>
</head>
<body onload="createCode()">
<form action="#">
    <input type="text" id="input1" /> <input type="text" onclick="createCode()" readonly="readonly" id="checkCode" class="unchanged" style="width: 80px" /><br />
    <input id="Button1" onclick="validate();" type="button" value="确定" />
</form>
</body>
</html>

3 js 实现图片刷新验证码看不清换一张

【需求】

html+js实现html中一个图片刷新但是整个页面不刷新，或者是验证码刷新。

不使用jsp，不使用ajax，不使用js框架。

【原理】

当一个<img>的src改变时，页面会自动刷新这个<img>

【实现代码】

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">  
<html>  
  <head>  
    <title>test</title>  
    <script type="text/javascript">  
        function reImg(){  
            var img = document.getElementById("Img");  
            img.src = "Img?rnd=" + Math.random();  
        }  
    </script>  
  </head>  
    
  <body>  
    <center>  
        <img id="Img" src="Img" alt="验证码"  />  
        <a href="#" onclick="reImg();">看不清，换一张</a>  
    </center>  
  </body>  
</html>