Implementation and technical analysis of verification code generated by js

Implementation and technical analysis of verification code generated by js_javascript skills

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Release： 2016-05-16 16:36:12

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Share with you a piece of js code to generate and verify the verification code

<!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>
<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 = 6;//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>

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As we all know, js is client-side, so does it make sense to do all the verification on the client side? Or must the verification code generated from the server be secure? Is the verification code generated by the front end safe?

The verification code is dynamic, but must be recognized by the client and return the correct value for normal verification. This is a process issue. If it is js, it is verified on the client, which is basically the same! ! ! It is best to generate it on the server, verify it on the client, confirm it on the server, and browse it normally. Such a process is foolproof

So, this article is just a technical discussion, please do not use it in actual production projects