js编写验证码以及验证

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


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


<script>

//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{
alert('验证码正确');
}
}

//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();
}
</script>