JS 实现随机验证码功能

 <div> 
  <input type = "text" id = "input" value="" /> 
  <input type = "button" id="code" onclick="createcode()"/> 
  <input type = "button" value = "验证" onclick = "validate()"/> 
 </div> 

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

//设置一个全局的变量，便于保存验证码
 var code;
 function createcode(){
  //首先默认code为空字符串
  code = '';
  //设置长度，这里看需求，我这里设置了4
  var codelength = 4;
  var codev = document.getelementbyid('code');
  //设置随机字符
  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');
  //循环codelength 我设置的4就是循环4次
  for(var i = 0; i < codelength; i++){
   //设置随机数范围,这设置为0 ~ 36
    var index = math.floor(math.random()*36);
    //字符串拼接 将每次随机的字符 进行拼接
    code += random[index]; 
  }
  //将拼接好的字符串赋值给展示的value
  codev.value = code;
 }
 //下面就是判断是否== 的代码，无需解释
 function validate(){
  var ovalue = document.getelementbyid('input').value.touppercase();
  if(ovalue ==0){
   alert('请输入验证码');
  }else if(ovalue != code){
   alert('验证码不正确，请重新输入');
   ovalue = ' ';
   createcode();
  }else{
   window.open('http://www.baidu.com','_self');
  }
 }
 //设置此处的原因是每次进入界面展示一个随机的验证码，不设置则为空
 window.onload = function (){
  createcode();
 }