Dropdown undefined javascript form validation error

Question

I have the following sample of html code:

<form id="registration" action="process.php" onsubmit="return validateForm()" method="post">
    <label for="range_date" class="form">Select Range Date</a></label>
    <select name="range_date">
        <option value="" style="display:none;"></option>
        <option value="June 27th 2014 6:00pm">June 27th 2014 6:00pm</option>
        <option value="June 27th 2014 8:00pm">June 27th 2014 8:00pm</option>
    </select>
</form >

And the following sample js code:

if (document.forms["registration"]["range_date"] != 'undefined') 
{
    var range_date=document.forms["registration"]["range_date"].value;
    if (range_date==null || range_date=="")
    {  
        alert("Please select a Range Date");
        return false;
    }  
}

I get an error in firebug stating: "document.forms.registration.range_date is undefined" but I don't expect it to reach the inside of the if statement. Any thoughts?

Try document.forms["registration"]["range_date"] != null && document.forms["registration"]["range_date"] != undefined — user1071777
– user1071777, Commented Jun 16, 2014 at 21:22
Your problem does not originate from the sample you provided, eventhough it's not 100% correct. It runs: jsfiddle.net/Vznaw — Jacco
– Jacco, Commented Jun 16, 2014 at 21:28

epascarello · Accepted Answer · 2014-06-16 21:22:16Z

1

That is because 'undefined' != undefined.

Just use a truthy check

if (document.forms["registration"]["range_date"]) {

or drop the quotes

if (document.forms["registration"]["range_date"]===undefined) {

answered Jun 16, 2014 at 21:22

epascarello

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