JS Validation

Form validation normally used to occur at the server, after the client had entered all the necessary data and then pressed the Submit button. ... JavaScript provides a way to validate form's data on the client's computer before sending it to the web server.

Example of JavaScript Validation code:



    // JavaScript for disabling form submissions if there are invalid fields
    (function () {
    'use strict';

    window.addEventListener('load', function () {
    // Fetch all the forms we want to apply custom Bootstrap validation styles to
    var forms = document.getElementsByClassName('needs-validation');

    // Loop over them and prevent submission
    var validation = Array.prototype.filter.call(forms, function (form) {
    form.addEventListener('submit', function (event) {
    if (form.checkValidity() === false) {
    event.preventDefault();
    event.stopPropagation();
    }
    form.classList.add('was-validated');
    }, false);
    });
    }, false);
    })();