SOURCE

console 命令行工具 X clear

                    
>
console
let nameInput = document.querySelector('#name');
let emailInput = document.querySelector('#email');
let emailTip = document.querySelector('#emailTip');

function check(){
    let name = nameInput.value;
    let email = emailInput.value;
    let pattern = /^\S+@\S+\.\S+$/;

    if (name.length <2 || 
        !email.includes('@') ||         
        !email.includes('.') || 
        !pattern.test(email)){
        emailTip.classList.remove('hidden');
        emailInput.style.border = '2px solid red';
        }else{
        emailTip.classList.add('hidden');
        }
    }

nameInput.oninput = check;
emailInput.oninput = check;
<input id="name" placeholder="请输入姓名">
<input id="email" placeholder="请输入邮箱">
<p id= 'emailTip' class="hidden">输入内容错误</p>
.hidden {
  display: none;
}