

Xem demo ở đây : http://fandung.110mb.com/hide-show-email-field/show-radio.html
Hình minh họa:


Code HTML:
<!-- Radio elements -->
<input type="radio" name="newsletter" value="1" id="newsletter-1" onclick="javascript:toggle(1)" /><label for="newsletter-1">Yes</label>
<input type="radio" name="newsletter" value="1" id="newsletter-0" onclick="javascript:toggle(0)" checked="checked" /><label for="newsletter-2">No</label>
<!-- Hidden layer -->
<div id="email-field" style="display:none;">
<input type="text" id="email" />
Add your Email
</div>
Code Javascript:
<script type="text/javascript">
function toggle(status){
idStatus = status;
element =document.getElementById('email-field');
if(idStatus==0){
element.style.display='none';
} else {
element.style.display='block';
}
}
</script>