Date Validation Function (Month / Day And Year)

I am working on a series of functions that I keep getting asked about. The following three scripts do this:
--Date Validation
--Calculate Difference Between Dates
--Date Addition or Subtraction

I am sure that these have been done before, but I just filled the last 20 minutes by coding these. I only did a quick browser test, nothing extensive.
<script>
//Date Validation
function DateValid(mo, dy, yr){
TheDate = mo+"/"+dy+"/"+yr;
Date1 = new Date(TheDate)
D=Date1.getDate();
M=Date1.getMonth()+1;
Y=Date1.getYear();
[Code] .....