代码如下：
<!doctype html> <html lang="en"> <head> <meta charset="UTF-8"> <title>js验证码</title> <style type="text/css"> #code{ width:80px; height:30px; font-size:20px; font-family:Arial; font-style:italic; font-weight:bold; border:0; letter-spacing:2px; color:blue; } </style> </head> <body> <div> <input type = "text" id = "input"/> <input type = "button" /> <input type = "button" value = "验证"/> </div> <script type="text/javascript"> window.onload=function(){ var code=document.getElementById("code"); function change(){ // 验证码组成库 var arrays=new Array( '1','2','3','4','5','6','7','8','9','0', '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' ); // 重新初始化验证码 codes =''; // 随机从数组中获取四个元素组成验证码 for(var i = 0; i<4; i++){ // 随机获取一个数组的下标 var r = parseInt(Math.random()*arrays.length); codes += arrays[r]; } // 验证码添加到input里 code.value = codes; } change();//加载显示在页面上 code.onclick = change;//单击更换验证码 //单击验证 var check=document.getElementById("check"); var input=document.getElementById("input"); check.onclick=function(){ var inputCode = input.value.toUpperCase(); //取得输入的验证码并转化为大写 if(inputCode.length==0) { //若输入的验证码长度为0 alert("请输入验证码！"); //则弹出请输入验证码 } else if(inputCode!=codes.toUpperCase()) { //若输入的验证码与产生的验证码不一致时 alert("验证码输入错误！请重新输入"); //则弹出验证码输入错误 change();//刷新验证码 input.value="";//清空文本框 } else{ //输入正确时 alert("输入正确"); //弹出输入正确 } } } </script> </body> </html>