Form validation of the pattern if(f.value.length==0) is barely worthy of the name, and virtually useless, as even a single space, an X or a ? will return false, that is pass the validation. Numeric values, such as zip codes and phone numbers, should be validated as such. Ditto email addresses. This topic has been covered many times before in this forum.
All advice is supplied packaged by intellectual weight, and not by volume. Contents may settle slightly in transit.
All the code given in this post has been tested and is intended to address the question asked.
Unless stated otherwise it is not just a demonstration.
Last edited by Philip M; 09-30-2011 at 07:40 PM..