URL Encode and Decode in JavaScript

gistfile1.js

/**
	* rfc3986 compatable encode of a string
	*
	* @param {String} string
	*/
    self.urlEncode = function (string) {
		function hex(code) {
			var hex = code.toString(16).toUpperCase();
			if (hex.length < 2) {
				hex = 0 + hex;
			}
			return '%' + hex;
		}

		if (!string) {
			return '';
		}

		string = string + '';
		var reserved_chars = /[ \r\n!*"'();:@&=+$,\/?%#\[\]<>{}|`^\\\u0080-\uffff]/,
			str_len = string.length, i, string_arr = string.split(''), c;

		for (i = 0; i < str_len; i++) {
			if (c = string_arr[i].match(reserved_chars)) {
				c = c[0].charCodeAt(0);

				if (c < 128) {
					string_arr[i] = hex(c);
				} else if (c < 2048) {
					string_arr[i] = hex(192+(c>>6)) + hex(128+(c&63));
				} else if (c < 65536) {
					string_arr[i] = hex(224+(c>>12)) + hex(128+((c>>6)&63)) + hex(128+(c&63));
				} else if (c < 2097152) {
					string_arr[i] = hex(240+(c>>18)) + hex(128+((c>>12)&63)) + hex(128+((c>>6)&63)) + hex(128+(c&63));
				}
			}
		}
        return string_arr.join('');
    };

	/**
	* rfc3986 compatable decode of a string
	*
	* @param {String} string
	*/
	self.urlDecode = function (string){
		if (!string) {
			return '';
		}
		return string.replace(/%[a-fA-F0-9]{2}/ig, function (match) {
			return String.fromCharCode(parseInt(match.replace('%', ''), 16));
		});
	};

Why not use Javascript's encodeURIComponent() and decodeURIComponent() functions for URL encoding and decoding? Are they not rfc3986 compatible?