Проверка формы через JQuery: это не работает с JQuery. Последняя версия CDN (сеть доставки контента)?

Validating HTML forms is a very important aspect during form submission. jQuery helps in validating forms at client side. The following steps are required to validate a form.

Step 1: Create a Simple HTML Form
To create the form use the following code.
<h1>Fill out your information</h1>
<form id = "regForm" method = "post">
  <input type = "text" name = "fullname" id = "fullname" placeholder = "Your Full Name"/>
  <input type = "text" name = "email" id = "email" placeholder = "Email ID"/>
  <input type = "text" name = "mobileno" id = "mobileno" id = "mobileno" placeholder = "Mobile Number" maxlength = "10"/>
  <input type = "text" name = "address" id = "address" placeholder = "Address"/>
  <input type = "password" name = "password" id = "password" value = "" placeholder = "Password"/>
  <input type = "password" name = "repassword" id = "repassword" value = "" placeholder = "RetypePassword"/>
  <button name = "submit" type = "button" id = "btnvalidate">Click to Submit</button>
</form>

<script type = "text/javascript">

  //Find the values added in form using the id of each fields. The ".val()" function finds the value added in the form fields.
  var fullname = $('#fullname').val();
  var address = $('#address').val();
  var mobileno = $('#mobileno').val();
  var email = $('#email').val();
  var indexat = email.indexOf("@"); //Index of "@" in the email field
  var indexdot = email.indexOf("."); //Index of "." in the email field
  var password = $('#password').val();
  var repassword = $('#repassword').val();
  
  //Function will execute when the button "Click to Submit" is clicked.
  $('#btnvalidate').click(function() {
	  
    //Blank field validation of fullname, mobile no and address. The function will generate an alert message if "fullname" or "mobile no" or "address" field is blank  
    if (fullname == '')
    {
	  alert('Please enter your Full Name');
	  $('#fullname').focus(); //The focus function will move the cursor to "fullname" field
    }
    else if (address == '')
    {
	  alert('Please enter your Address');
	  $('#address').focus();
    }
    else if (mobileno == '')
    {
	  alert('Please enter your Mobile Number');
	  $('#address').focus();
    }
    
    //Validation of valid email address. The function will generate an alert message if "email" field is blank or incorrect
    else if (indexat < 1 || (indexdot-indexat) < 2)
    {
	  alert('Please enter a valid Email Id');
	  $('#email').focus();
    }
    
    //Validation of password. The function will generate an alert message if "password" field is not same as "retype password".
    else if (password == '' && password != repassword)
    {
	  alert('Password and Retype password donot match');
	  $('#repassword').focus();
    }
  });
  
</script>