javascript utf8 encode and decode

JavascriptUTF8EncodeDecode.js

//+ Jonas Raoni Soares Silva
//@ http://jsfromhell.com/geral/utf-8 [v1.0]

UTF8 = {
	encode: function(s){
		for(var c, i = -1, l = (s = s.split("")).length, o = String.fromCharCode; ++i < l;
			s[i] = (c = s[i].charCodeAt(0)) >= 127 ? o(0xc0 | (c >>> 6)) + o(0x80 | (c & 0x3f)) : s[i]
		);
		return s.join("");
	},
	decode: function(s){
		for(var a, b, i = -1, l = (s = s.split("")).length, o = String.fromCharCode, c = "charCodeAt"; ++i < l;
			((a = s[i][c](0)) & 0x80) &&
			(s[i] = (a & 0xfc) == 0xc0 && ((b = s[i + 1][c](0)) & 0xc0) == 0x80 ?
			o(((a & 0x03) << 6) + (b & 0x3f)) : o(128), s[++i] = "")
		);
		return s.join("");
	}
};

This solution doesn’t work correctly for astral symbols. e.g. UTF8.encode('\uD834\uDF06').

'\uD834\uDF06' is U+1D306.

The result should be F0 9D 8C 86.

// …but with the current implementation: 
UTF8.encode('\uD834\uDF06') == '\xF0\x9D\x8C\x86' // false

Decoder with full Unicode support: https://gist.github.com/pascaldekloe/62546103a1576803dade9269ccf76330