Simple Korean romanization from http://www.tckerrigan.com/Misc/Korean+romanizer

romanize.js

var choseongInit = 'G;GG;N;D;DD;L;M;B;BB;S;SS;;J;JJ;C;K;T;P;H';
var jungseongInit = 'A;AE;YA;YAE;EO;E;YEO;YE;O;WA;WAE;OE;YO;U;WEO;WE;WI;YU;EU;YI;I';
var jongseongInit = ';G;GG;GS;N;NJ;NH;D;L;LG;LM;LB;LS;LT;LP;LH;M;B;BS;S;SS;NG;J;C;K;T;P;H';

function Romanize()
{
	choseongList = choseongInit.split(';');
	jungseongList = jungseongInit.split(';');
	jongseongList = jongseongInit.split(';');

	strKorean = document.getElementById('idKorean').value;
	outStr = '';
	for (i = 0; i < strKorean.length; i++)
		{
		charCode = strKorean.charCodeAt(i);
		if (charCode < 44032 || charCode > 44032 + 11172)
			{
			outStr += String.fromCharCode(charCode);
			continue;
			}
		n = 44032;
		for (choseong = 0;; choseong++)
			{
			n += jungseongList.length * jongseongList.length;
			if (n > charCode)
				break;
			}
		n -= jungseongList.length * jongseongList.length;
		for (jungseong = 0;; jungseong++)
			{
			n += jongseongList.length;
			if (n > charCode)
				break;
			}
		n -= jongseongList.length;
		jongseong = charCode - n;
		outStr += choseongList[choseong] + jungseongList[jungseong] + jongseongList[jongseong];
		}
	document.getElementById('idRoman').innerHTML = outStr.toLowerCase();
}