Multi step form with email validation trouble

Question

I am implementing this multi step form with validation on my website: https://www.w3schools.com/howto/howto_js_form_steps.asp

All works perfectly, I modified the code slightly to also validate select drop downs.

My problem is that I can't get the email address input to validate as an email address. It validates if my email address field has soemthing in it, but not whether it is an actual email address or not.

This is my working js:

var currentTab = 0; // Current tab is set to be the first tab (0)
showTab(currentTab); // Display the current tab

function showTab(n) {
// This function will display the specified tab of the form ...
var x = document.getElementsByClassName("tabStep");
x[n].style.display = "block";
// ... and fix the Previous/Next buttons:
if (n == 0) {
document.getElementById("prevBtn").style.display = "none";
} else {
  document.getElementById("prevBtn").style.display = "inline";
}
if (n == (x.length - 1)) {
  document.getElementById("nextBtn").innerHTML = "Submit";
} else {
  document.getElementById("nextBtn").innerHTML = "Next";
}
// ... and run a function that displays the correct step indicator:
fixStepIndicator(n)
}

function nextPrev(n) {
// This function will figure out which tab to display
var x = document.getElementsByClassName("tabStep");
// Exit the function if any field in the current tab is invalid:
if (n == 1 && !validateForm()) return false;
// Hide the current tab:
x[currentTab].style.display = "none";
// Increase or decrease the current tab by 1:
currentTab = currentTab + n;
// if you have reached the end of the form... :
if (currentTab >= x.length) {
//...the form gets submitted:
document.getElementById("mobileReg").submit();
return false;
}
// Otherwise, display the correct tab:
showTab(currentTab);
}

function validateForm() {
// This function deals with validation of the form fields
var x, y, z, i, valid = true;
x = document.getElementsByClassName("tabStep");
y = x[currentTab].getElementsByTagName("input");
z = x[currentTab].getElementsByTagName("select");

// A loop that checks every input field in the current tab:
for (i = 0; i < y.length; i++) {
// If a field is empty...
if (y[i].value == "") {
  // add an "invalid" class to the field:
  y[i].className += " invalid";
  // and set the current valid status to false:
  valid = false;
 }
}
for (i = 0; i < z.length; i++) {
// If a field is empty...
if (z[i].value == "") {
  // add an "invalid" class to the field:
  z[i].className += " invalid";
  // and set the current valid status to false:
  valid = false;
}
}
// If the valid status is true, mark the step as finished and valid:
if (valid) {
  document.getElementsByClassName("step")[currentTab].className += " finish";
}
return valid; // return the valid status
}


function fixStepIndicator(n) {
// This function removes the "active" class of all steps...
var i, x = document.getElementsByClassName("step");
for (i = 0; i < x.length; i++) {
  x[i].className = x[i].className.replace(" active", "");
}
//... and adds the "active" class to the current step:
x[n].className += " active";
}

I tried incorporating the following into the validateForm() fuction, but just couldn't get i to work:

function ValidateEmail(inputText)
{
var mailformat = /^\w+([\.-]?\w+)*@\w+([\.-]?\w+)*(\.\w{2,3})+$/;
if(inputText.value.match(mailformat))
{
document.form1.text1.focus();
return true;
}
else
{
alert("You have entered an invalid email address!");
document.form1.text1.focus();
return false;
}
}

I also looked at: How to validate an email address in JavaScript? but just can't seem to implement it in this script without killing it.

Any pointers would be much appreciated

Many thanks

D