checkDate in Javascript

I know there are lots of implementations of date validation in Javascript out there, but I've just started learning Javascript and wanted to share this implementation with you, so here are my first two little javascript cents:

function checkDate(month, day, year)
{
  var monthLength = 
    new Array(31,28,31,30,31,30,31,31,30,31,30,31);

  if (!day || !month || !year)
    return false;

  // check for bisestile year
  if (year/4 == parseInt(year/4))
    monthLength[1] = 29;

  if (month < 1 || month > 12)
    return false;

  if (day > monthLength[month-1])
    return false;
  
  return true;
}