Quick date validation with a Regular Expression

/(?:19|20)[0-9]{2}-(?:(?:0[1-9]|1[0-2])-(?:0[1-9]|1[0-9]|2[0-8])|(?:(?!02)(?:0[1-9]|1[0-2])-(?:29|30))|(?:(?:0[13578]|1[02])-31))/

Here's the breakdown of what it does:

Given a date format of YYYY-MM-DD (standard MySQL date format and easiest format for sorting) it makes sure that

1. the year is numeric and starts with 20 or 19, and
2. the month is numeric and is either
   1. between 01 - 12 and followed by a numeric day value between 01-28;
   2. between 01 - 12 but not 02 and followed by a day value of 29 or 30; or
   3. one of 01,03,05,07,08,10,12 and followed by a day value of 31

I have left out Feb. 29th so that you are forced to do a secondary leap year check.

JavaScript roman numeral converter.

Here's the JavaScript Roman Numeral Conversion functions I alluded to in the last post.

//each numeral, starting with the largest
var numerals = {
  "M":1000,
  "CM":900,
  "D":500,
  "CD":400,
  "C":100,
  "XC":90,
  "L":50,
  "XL":40,
  "X":10,
  "IX":9,
  "V":5,
  "IV":4,
  "I":1
};
function RomanToDecimal(roman) {
  //the roman numeral value
  var _v = roman.toUpperCase();
  //this holds the decimal equivalent
  var _d = 0;
  //if the roman value contains more than the allowed letters return Not a Number
  if (!_v.match(/^[MDCLXVI]+$/)) return NaN;
  //for each roman numeral
  for (_n in numerals) {
    //while this numeral is at the front of the passed string
    while (_v.match(new RegExp("^"+_n))) {
      //add the numeral's decimal value to the decimal equivalent
      _d += numerals[_n];
      //and pop off the numeral found
      _v = _v.substr(_n.length);
    }
  }
  // still letters left. Improper sequencing. return Not a Number
  if (_v.length) return NaN;
  //otherwise, return the decimal equivalent
  else return _d;
}

function DecimalToRoman(num) {
  //the decimal equvalent
  var _d = parseInt(num);
  //this will hold the roman value
  var _r = '';
  //for each roman numeral
  for(var _n in numerals) {
    // get the number of times (if any) it divides into the decimal value
    var _x =Math.floor(_d/numerals[_n]);
    // if it does divide into the decimal value
    if (_x) {
      // subtract that amount from the decimal value
      _d -= (_x*numerals[_n]);
      //and add the appropriate number of numerals to the roman value
      for(var a=0;a<_x;a++) {
        _r += _n;
      }
    }
    // if the decimal value now equals zero, stop building our number
    if (!_d) break;
  }
  return _r;
}
DecimalToRoman(RomanToDecimal("MCCLXXVIIII"));

Difference between using Object as associative array in Flash AS3 and JavaScript

As I was porting a Roman number converter (I will post it shortly) I had written in JavaScript to AS3 and ran into an interesting "quirk" of the AS3 Object class. I doesn't keep the keys in the same order that they were declared. The code used an Object literal as an associative array; holding each roman "digit" along with it's decimal equivalent in descending order by value. I'd then use a for ... in loop to cycle through the object. In JavaScript I'd get the values in the same order they had been generated. AS3 seems to be a little more cavalier. The following code in Javascript:

var o = {
 "name1":1,
 "name2":1,
 "name3":1,
 "name4":1,
 "name5":1
};
var a=0;
for (var n in o) {
 document.write(" o " + a + ":"+n);
 a++; 
}

produces this result in all major browsers (Firefox 3.5, IE 8, Safari 4, Opera 9.54, Chrome 2):
o 0:name1 o 1:name2
o 2:name3
o 3:name4
o 4:name5

However, using the following code in the Flash IDE

var o:Object = {
 "name1":1,
 "name2":1,
 "name3":1,
 "name4":1,
 "name5":1
};
var a:uint = 0
for (var n:String in o) {
 trace(" o " + a + ":"+n);
 a++;
}

resulted in the following trace result:
o 0:name4
o 1:name5
o 2:name1
o 3:name2
o 4:name3
Oddly, it seemed to produce the exact same order each time I ran it. I tried it with a Dictionary, to see if the made a difference, but results were similar. I tried different values, to try and find a reason for the ordering -- to no avail. If someone knows why it's consistently picks the same random order, I'd love to know.