form name, password, email required js code example

Example 1: how to set validation for email in javascript

<script language="javascript">

function checkEmail() {

    var email = document.getElementById('txtEmail');
    var filter = /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/;

    if (!filter.test(email.value)) {
    alert('Please provide a valid email address');
    email.focus;
    return false;
 }
}</script>

Example 2: Javascript validate password

let pattern = new RegExp("^(?=(.*[a-zA-Z]){1,})(?=(.*[0-9]){2,}).{8,}$"); //Regex: At least 8 characters with at least 2 numericals
    let inputToListen = document.getElementById('pass-one'); // Get Input where psw is write
    let valide = document.getElementsByClassName('indicator')[0]; //little indicator of validity of psw

    inputToListen.addEventListener('input', function () { // Add event listener on input
        if(pattern.test(inputToListen.value)){
            valide.innerHTML = 'ok';
        }else{
            valide.innerHTML = 'not ok'
        }
    });