以下是JavaScript的表单验证功能，可根据JS代码编写出你想要的HTML和CSS的代码。
关于正则表达式的使用，以及常用的正则表达式，笔者目前还在整理中，后期整理完成后，会将链接放在下面，供大家一起学习。
//1.声明变量
var emailObj;
var usernameObj;
var passwordObj;
var confirmObj;
var emailMsg;
var usernameMsg;
var passwordMsg;
var confirmMsg;
//页面加载之后，获取页面中的对象
window.onload = function() {
emailObj = document.getElementById("email");
usernameObj = document.getElementById("username");
passwordObj = document.getElementById("password");
confirmObj = document.getElementById("confirm");
emailMsg = document.getElementById("emaileMsg");
usernameMsg = document.getElementById("usernameMsg");
confirmMsg = document.getElementById("confirmMsg");
};
//3.检验整个表单
function checkForm() {
var bEmail = checkEmail();
var bUsername = checkUsername();
var bPassword = checkPassword();
var bConfirm = checkCondfirm();
return bUsername && bPassword && bConfirm && bEmail;
}
//4.验证邮箱
function checkEmail() {
var regex = /^([a-zA-Z]|[0-9])(\w|\-)+@[a-zA-Z0-9]+\.([a-zA-Z]{2,4})$/;
var value = emailObj.value;
var msg = "";
if(!value) {
msg = "邮箱必须填写";
} else if (!regex.test(value)) {
msg = "邮箱格式不合法";
}
emailMsg.innerHTML = msg;
emailObj.parentNode.parentNode.style.color = msg == ""?"black":"red";
return msg == "";
}
//5.验证用户名‘
function checkUsername() {
var regex = /^[a-zA-Z0-9_-]\w{0,9}$/; //字母数字下划线1-10位，不能是数字开头
var value = usernameObj.value; //获取usernameObj中的文本
var msg = ""; //最后的提示小事，默认为空
//如果用户名是null或"",!value的值为false，如果不为空 !value值为true
if(!value) {
msg = "用户名必须填写";
} else if (regex.test(value)) {
msg = "用户名不合法";
}
usernameMsg.innerHTML = msg;
usernameObj.parentNode.parentNode.style.color = msg == ""?"black":"red";
return msg == ""; //如果提示消息为空则代表没出错，返回true
}
//6.验证密码
function checkPassword() {
var regex = /^.{6,16}$/; //任意字符，6-16位
var value = passwordObj.value;
var msg = "";
if(!value) {
msg = "密码必须填写";
} else if (!regex.test(value)) {
msg = "密码不合法";
}
passwordMsg.parentNode.parentNode.style.color = msg == ""?"black":"red";
return msg == "";
}
//7.验证确认密码
function checkCondfirm() {
var passwordValue = passwordObj.value;
var confirmValue = confirmObj.value;
var msg = "";
if(!confirmValue) {
msg = "确认密码填写";
} else if (passwordValue != confirmValue) {
msg = "密码必须保持一致";
confirmMsg.innerHTML = msg;
confirmObj.parentNode.parentNode.style.color = msg == ""?"black":"red";
return msg == "";
}
以下代码是简单的测试邮箱是否匹配成功的代码，可根据下面来实现具体的逻辑
<!DOCTYPE html>
<html lang="zh-CN">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<input type="text" placeholder="请输入邮箱" id="email">
</body>
<script>
email.onchange = function(){
var email = this.value;
var reg = /^([a-zA-Z]|[0-9])(\w|\-)+@[a-zA-Z0-9]+\.([a-zA-Z]{2,4})$/;
if(reg.test(email)){
alert("邮箱格式正确");
}else{
alert("邮箱格式不正确");
}
}
</script>
</html>