How to give validation in two textbox

Question

I have a problem in this script. My function about given validation in two textbox. anybody here can help me?

My function:

<script>
          window.onload = function () {
            document.getElementById("pass").onchange = validatePassword;
            document.getElementById("rp_pass").onchange = validatePassword;
        };
        function validatePassword()
        {
            var pass2=document.getElementById("pass").value;
            var pass1=document.getElementById("rp_pass").value;
            if(pass1!=pass2)
                document.getElementById("rp_pass").setCustomValidity("Passwords Don't Match");
            else
                document.getElementById("rp_pass").setCustomValidity('');
                    //empty string means no validation error
        }

  </script>

Answer 1

Apply same class on each textbox and apply setCustomValidity on class as below hope it helps

  window.onload = function () {
                    document.getElementById("pass").onchange = validatePassword;
                    document.getElementById("rp_pass").onchange = validatePassword;
                };
                function validatePassword()
                {
                    var pass2=document.getElementById("pass").value;
                    var pass1=document.getElementById("rp_pass").value;
                    if(pass1!=pass2)
                      document.getElementsByClassName("customvalidity").setCustomValidity("Passwords Don't Match");
                    else
                                   

                        document.getElementsByClassName("customvalidity").setCustomValidity('');
                            //empty string means no validation error
                }

    <input type="text" value="" id="pass" class="customvalidity"/>
<input type="text" value="" id="rp_pass" class="customvalidity" />