<div> 
  <input type = "text" id = "input" value="" /> 
  <input type = "button" id="code" onclick="createCode()"/> 
  <input type = "button" value = "驗(yàn)證" onclick = "validate()"/> 
 </div> 

 #code{ 
    font-family:Arial; 
    font-style:italic; 
    font-weight:bold; 
    border:0; 
    letter-spacing:2px; 
    color:blue; 
   }

//設(shè)置一個(gè)全局的變量，便于保存驗(yàn)證碼
 var code;
 function createCode(){
  //首先默認(rèn)code為空字符串
  code = '';
  //設(shè)置長度，這里看需求，我這里設(shè)置了4
  var codeLength = 4;
  var codeV = document.getElementById('code');
  //設(shè)置隨機(jī)字符
  var random = 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');
  //循環(huán)codeLength 我設(shè)置的4就是循環(huán)4次
  for(var i = 0; i < codeLength; i++){
   //設(shè)置隨機(jī)數(shù)范圍,這設(shè)置為0 ~ 36
    var index = Math.floor(Math.random()*36);
    //字符串拼接 將每次隨機(jī)的字符 進(jìn)行拼接
    code += random[index]; 
  }
  //將拼接好的字符串賦值給展示的Value
  codeV.value = code;
 }
 //下面就是判斷是否== 的代碼，無需解釋
 function validate(){
  var oValue = document.getElementById('input').value.toUpperCase();
  if(oValue ==0){
   alert('請(qǐng)輸入驗(yàn)證碼');
  }else if(oValue != code){
   alert('驗(yàn)證碼不正確，請(qǐng)重新輸入');
   oValue = ' ';
   createCode();
  }else{
   window.open('http://www.baidu.com','_self');
  }
 }
 //設(shè)置此處的原因是每次進(jìn)入界面展示一個(gè)隨機(jī)的驗(yàn)證碼，不設(shè)置則為空
 window.onload = function (){
  createCode();
 }