Small shim for formatting Pikaday dates as YYYY-MM-DD without moment.js

moment_shim.js

// Would be ridiculous to pull in the entire moment.js library for this
window.moment = function(dateString) {

  var date = new Date(dateString);

  var format = function() {
    return date.getFullYear() + '-' +
             ('0' + (date.getMonth() + 1)).slice(-2) + '-' +
             ('0' + date.getDate()).slice(-2);
  };

  return {
    format: format,
    toDate: format
  }
};

When I use this, it works visually (as in the date is displayed in a nice format in the input field). But if you get the value from the field, it isn't a dateobject anymore. And you would have to parse it everytime manually again. Or am I missing something?