原生验证码 不区分大小写

var oText = document.getElementById("text");
var oBtn = document.getElementById("btn");
var val = "";
creatCode()
function creatCode(){
var arr = ['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','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']
val = "";
for (var i=0;i<4;i++) {
var index = Math.floor(Math.random()*62)
val += arr[index];
}
oBtn.value = val;
}
function validate(){
var inputcode = document.getElementById("text").value;
console.log(inputcode.toLowerCase())
if(val.length == 0){
alert("请输入验证码")
}else if(inputcode.toLowerCase() != val.toLowerCase()){
alert("验证码错误")
creatCode();
return false;
}else{
alert("成功！")
return true;
}
}