It depends on what you are wanting to do.
You could have just as easily use the toGMTString() or the UTC equivalent to obtain a formatted string and using .slice() to cut out what you needed.
if you want to use the above then
var d=new Date();
and applying the value of d to your output field results in a value like "Fri Jul 19 2013 09:31:00 GMT+0100 (GMT Daylight Time)"
using var d=new Date().toGMTString(); results in a string like "Fri, 19 Jul 2013 08:32:19 GMT"
using var d=new Date().toUTCString(); results in a string like "Fri, 19 Jul 2013 08:32:19 GMT"
Your script can be easily compressed by using the "with" clause down to...
function chgit() {
with( new Date() );
document.getElementById("Date_Resolved").value = [getMonth()+1,getDate(),getFullYear()].join("/");
}