如何通过使用OnChange Javascript HTML验证表单

Question

I am trying to do an extra check on a form using OnChange so an alert box appears if the text if equal to a specific value BEFORE the form is submitted. If i remove the If value then the alert box WILL appear but its not coming up if the field is set to 'No Longer Required'

<script type="text/javascript">
/*<![CDATA[*/
function extracheck(s) {

if (s.value == "No Longer Required"){
alert("message here");
}
}

/*]]>*/
</script>

 <form id="form2" name="form2" method="post" action="returnprocess.asp" onSubmit="return     validateForm(this)">
  <select name="Reason1" class="textfieldmedium" id="Reason1" onchange="extracheck(this)">
                        <option selected="selected">Reason for Return</option>
                       <option>No Longer Required</option>
                        <option>Duplicated Order</option>
                        <option>Choice of Two</option>
                        <option>Incorrectly Supplied</option>
                        <option>Incorrect for Application</option>
                        <option>Incorrectly Packaged</option>
                        <option>Late Delivery</option>
                        <option>Incorrectly Picked</option>
                        <option>Never Ordered</option>
                        <option>Surcharge Unit</option>
                        <option>Damaged</option>
                        <option>Poor Fitment</option>
                          </select>
      </form>

Why isnt the alert box coming up when there is an IF statement ?

Answer 1

You can do:

function extracheck(s) {
    var e = document.getElementById("Reason1");
    if (e.options[e.selectedIndex].value == "No Longer Required") {
        alert("message here");
    }
}

Demo: http://jsbin.com/lotebiho/1/

Answer 2

Alert is coming because function is executing every time and not on selection

try this,

<script>
    $(document).ready(function() {
        $("#Reason1").select(function() {
            if ($(".textfieldmedium").val() == "No Longer Required") {
                alert("Message here");
            }
        )};
    )};
</script>