Javascript form validation on dynamic forms

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I have this code: [embed=snippet 8161981]

This validates a form 'extra1' and 'extra2'. The problem is, these are dynamic, and it is possible that those forms never exist. Or that just 'extra1' exists and 'extra2' doesn't.

Javascript doesn't like this, it tries of course to run the code and if it tries to validate a form which doesn't exist, it falls over.

I am trying to come up with a 'catch' which will only run the code if that particular form exists, and skip it if not.

Is there a good way to do this?

if ((document.extra1.title1.value ==="") || (document.extra1.firstname1.value==="") || (document.extra1.surname1.value==="") || (document.extra1.bags1.value==="") ||(document.extra1.bags1.value > 3) || (IsNumeric(document.extra1.title1.value)) || (IsNumeric(document.extra1.firstname1.value)) || (IsNumeric(document.extra1.surname1.value)) || (!IsNumeric(document.extra1.bags1.value)))
{
document.getElementById("error").innerHTML="You need to fill in all details for Extra Passenger 1. Ensure text and numerals have been used as appropiate. You can have a maximum of three bags per passenger.";
valid = false;
}


else if ((document.extra2.title2.value ==="") || (document.extra2.firstname2.value==="") || (document.extra2.surname2.value==="") ||(document.extra2.bags2.value > 3) || (IsNumeric(document.extra2.title2.value)) || (IsNumeric(document.extra2.firstname2.value)) || (IsNumeric(document.extra2.surname2.value)) || (!IsNumeric(document.extra2.bags2.value)))
{
document.getElementById("error").innerHTML="You need to fill in all details for Extra Passenger 2. Ensure text and numerals have been used as appropiate. You can have a maximum of three bags per passenger.";
valid = false;
}

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Zone: general
Tags: Javascript HTML
Participating Experts: 3
Solution Grade: A