Disabled HTML Form and Javascript

[kbjradmin]

i have an html form. in it, there is a list of radio buttons, the last of which is 'other'. i have a text input that is to be disabled unless the 'other' radio button is selected. however, i can't seem to get the javascript to work.

here's the form:

<form name="contact" action="process.php" method="post">

<label class="text">Name:<input class="name" name="name" type="text" value="" /></label><br />

<label class="text">Email:<input class="email" name="email" type="text" value="" /></label><br />

<label class="text">Subject:<input class="sub" name="sub" type="text" value="" /></label><br />

<label class="text">Purpose:</label><br />

<label class="button"><input class="purpose" id="1" name="purpose" type="radio" value="Job Offer" onchange="radio_checker();" />Job Offer</label><br />

<label><input class="purpose" id="2" name="purpose" type="radio" value="Question/Comment" onchange="radio_checker();" />Question/Comment</label><br />

<label><input class="purpose" id="3" name="purpose" type="radio" value="Other" onchange="radio_checker();" />Other</label>

<input class="purposeOther" id="4" name="other" type="text" value="" disabled="true" /><br />

<label class="msg">Message:<textarea class="msg" name="msg" value=""></textarea></label>

<a href="javascript:submit();" class="submit">Send</a>
<a href="javascript:reset();" class="reset">Reset</a>

</form>

and the javascript:

function radio_checker() {
	if (document.contact.3.checked) {
		document.contact.purposeOther.disabled = false;
		document.contact.purposeOther.focus();
	}
	else {
		document.contact.purposeOther.disabled = true;
	}
}

please help.

[nightscream]

this should work
document.contact.[name].attribute
[name] can only be the value of the attribute name, not id or class. if you want to use id or class use a getElementbyID function or getElementsByClassName

function radio_checker() {
	if (document.getElementById("3").checked == true) {
		document.contact.other.disabled = false;
		document.contact.other.focus();
	}else {
		document.contact.other.disabled = true;
	}
}

[kbjradmin]

thank you very much nightscream.