- Add an id to your checkbox:
<input name='oth' id='oth'

- Add an id to your textbox:
<input type='text' name='other' id='other'

- Use this to checked whether the 'other' textbox is selected:
document.getElementById('oth').checked

- Slight change to aso's suggestion, which will work on if textfield.value is empty or null
(textfield.value || '').length <= 0

- Another change to aso's suggestion: checked AND empty (not OR)

- Then you end up with this:

Code: Select all

if(document.getElementById('oth').checked && (document.getElementById('other').value || '').length <= 0) {
 return false;
}

You should be able to make this work now...