scriptTrainerUpdate.js

document.getElementById('myFormTrainer').addEventListener('submit', function (event) {
    var firstName = document.getElementById("firstName");
    var lastName = document.getElementById("lastName");
    var subject = document.getElementById("subject");
    var sameMessage = "You did n't make any changes";
    //var emptyMessage = "You must fill all the fields";
    //var emptyFirstName = "You should fill the empty field****"
    var defaultFirstName = firstName.defaultValue;
    var currentFirstName = firstName.value;
    var defaultLastName = lastName.defaultValue;
    var currentLastName = lastName.value;
    var defaultSubject = subject.defaultValue;
    var currentSubject = subject.value;


    if (currentFirstName === defaultFirstName && currentLastName === defaultLastName && currentSubject === defaultSubject) {

        document.getElementById("fullInputs").innerHTML = sameMessage;
        event.preventDefault();
    } else {
        document.getElementById("fullInputs").innerHTML = "";
        var pattern = /^[A-Z]+[A-Za-z]+$/;
        var firstNameFormat = pattern.test(firstName.value);
        var lastNameFormat = pattern.test(lastName.value);

        if (firstNameFormat !== true || firstName.value.length < 3 || firstName.value.length > 50) {
            var message = "The name should start with capital letter, contain only letters MIN 3 and MAX 50";
            document.getElementById("firstNameValidation").innerHTML = message;
            event.preventDefault();
        } else {
            document.getElementById("firstNameValidation").innerHTML = "";
        }
        if (lastNameFormat !== true || lastName.value.length < 3 || firstName.value.length > 50) {
            var message = "The name should start with capital letter, contain only letters MIN 3 and MAX 50";
            document.getElementById("lastNameValidation").innerHTML = message;
            event.preventDefault();
        } else {
            document.getElementById("lastNameValidation").innerHTML = "";
        }

        var patternSubject = /^[A-Z]/;;
        var subjectFormat = patternSubject.test(subject.value);
        if (subjectFormat !== true || subject.value.length > 50) {
            var message = "The subject should start with capital letter and 50 characters MAX";
            document.getElementById("subjectValidation").innerHTML = message;
            event.preventDefault();
        } else {
            document.getElementById("subjectValidation").innerHTML = "";
        }
    }
});