Char extensions convert between characters and decimal numeric character references. Extends string prototype with the following methods with two methods: char2dec (convert character to decimal) and dec2char (convert decimal to character).

/**
 * Char extensions convert between characters and decimal Numeric Character
 * References.
 *
 * Extends string prototype with the following methods:
 * char2dec, dec2char
 *
 * This extensions doesn't depend on any other code or overwrite existing
 * methods. The Initial Developer of the Original Code is unknown.
 *
 * Contributor(s):
 * Harald Hanek <harald.hanek@gmail.com>
 * Copyright (c) 2007 Harald Hanek (http://js-methods.googlecode.com)
 * Dual licensed under the MIT (http://www.opensource.org/licenses/mit-license.php)
 * and GPL (http://www.gnu.org/licenses/gpl.html) licenses.
 *
 * @author Harald Hanek
 * @version 0.9
 * @lastchangeddate 10. October 2007 18:00:46
 * @revision 876
 */

(function() {

    var unicode = {

        dec2hex: function(ts) {
            return (ts + 0).toString(16).toUpperCase();
        },

        dec2hex2: function(ts) {
            var hexequiv = new Array("0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "A", "B", "C", "D", "E", "F");
            return hexequiv[(ts >> 4) & 0xF] + hexequiv[ts & 0xF];
        },

        dec2hex4: function(ts) {
            var hexequiv = new Array("0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "A", "B", "C", "D", "E", "F");
            return hexequiv[(ts >> 12) & 0xF] + hexequiv[(ts >> 8) & 0xF] + hexequiv[(ts >> 4) & 0xF] + hexequiv[ts & 0xF];
        },

        convertCP2Char: function(ts) {
            var outputString = '';
            ts = ts.replace(/^\s+/, '');
            if (ts.length == 0)
                return "";
            ts = ts.replace(/\s+/g, ' ');
            var listArray = ts.split(' ');
            for (var i = 0; i < listArray.length; i++) {
                var n = parseInt(listArray[i], 16);
                if (n <= 0xFFFF)
                    outputString += String.fromCharCode(n);
                else if (n <= 0x10FFFF) {
                    n -= 0x10000;
                    outputString += String.fromCharCode(0xD800 | (n >> 10)) + String.fromCharCode(0xDC00 | (n & 0x3FF));
                } else
                    outputString += '!erreur ' + unicode.dec2hex(n) + '!';
            }
            return (outputString);
        },

        convertCP2DecNCR: function(ts) {
            var outputString = "";
            ts = ts.replace(/^\s+/, '');
            if (ts.length == 0)
                return "";
            ts = ts.replace(/\s+/g, ' ');
            var listArray = ts.split(' ');
            for (var i = 0; i < listArray.length; i++) {
                var n = parseInt(listArray[i], 16);
                outputString += ('&#' + n + ';');
            }
            return (outputString);
        },

        convertChar2CP: function(ts) {
            var outputString = "",
                haut = 0,
                n = 0;
            for (var i = 0; i < ts.length; i++) {
                var b = ts.charCodeAt(i);
                if (b < 0 || b > 0xFFFF)
                    outputString += '!erreur ' + unicode.dec2hex(b) + '!';

                if (haut != 0) {
                    if (0xDC00 <= b && b <= 0xDFFF) {
                        outputString += unicode.dec2hex(0x10000 + ((haut - 0xD800) << 10) + (b - 0xDC00)) + ' ';
                        haut = 0;
                        continue;
                    } else {
                        outputString += '!erreur ' + unicode.dec2hex(haut) + '!';
                        haut = 0;
                    }
                }

                if (0xD800 <= b && b <= 0xDBFF)
                    haut = b;
                else
                    outputString += unicode.dec2hex(b) + ' ';
            }
            return (outputString.replace(/ $/, ''));
        },

        convertDecNCR2CP: function(ts) {
            var outputString = '';
            ts = ts.replace(/\s/g, '');
            var listArray = ts.split(';');
            for (var i = 0; i < listArray.length - 1; i++) {
                if (i > 0)
                    outputString += ' ';
                var n = parseInt(listArray[i].substring(2, listArray[i].length), 10);
                outputString += unicode.dec2hex(n);
            }
            return (outputString);
        }
    };

    /**
     * Convert Character to Decimal.
     *
     * @example "JavaScript".char2dec();
     * @result "&#74;&#97;&#118;&#97;&#83;&#99;&#114;&#105;&#112;&#116;"
     *
     * @name char2dec
     * @return String
     */
    if (!String.prototype.char2dec)
        String.prototype.char2dec = function() {
            return unicode.convertCP2DecNCR(unicode.convertChar2CP(this));
        };

    /**
     * Convert Decimal to Character.
     *
     * @example "&#74;&#97;&#118;&#97;&#83;&#99;&#114;&#105;&#112;&#116;".dec2char();
     * @result "JavaScript"
     *
     * @name dec2char
     * @return String
     */
    if (!String.prototype.dec2char)
        String.prototype.dec2char = function() {
            return unicode.convertCP2Char(unicode.convertDecNCR2CP(this));
        };
})();