JavaScript: Return date, if valid.

ba-dateifvalid.js

function dateIfValid(y, m, d) {
  var date = new Date(y, --m, d);
  return !isNaN(+date) && date.getFullYear() == y && date.getMonth() == m && date.getDate() == d && date;
}

ba-dateifvalid.min.js

function dateIfValid(y,m,d){var _=new Date(y,--m,d);return!isNaN(+_)&&_.getFullYear()==y&&_.getMonth()==m&&_.getDate()==d&&_}

I know the regexp could be mucked with, but you could do smth like below to reduce the day + year check.

function dateIfValid(y, m, d) {
  var date = new Date(y, --m, d);
  return (/(\d+) .*?(\d{4})/.exec(date)||'').slice(1) == d+','+y && date.getMonth() == m && date;
}

golf'ed to

function dateIfValid(y,m,d,_){
  return(/(\d+) .*?(\d{4})/.exec(_=new Date(y,--m,d))||'').slice(1)==d+','+y&&_.getMonth()==m&&_
}