Decode JavaScript UTF-16 arrays

utf-16.js

// http://www.ietf.org/rfc/rfc2781.txt
function decodeUtf16(w) {
    var i = 0;
    var len = w.length;
    var w1, w2;
    var charCodes = [];
    while (i < len) {
        var w1 = w[i++];
        if ((w1 & 0xF800) !== 0xD800) { // w1 < 0xD800 || w1 > 0xDFFF
            charCodes.push(w1);
            continue;
        }
        if ((w1 & 0xFC00) === 0xD800) { // w1 >= 0xD800 && w1 <= 0xDBFF
            throw new RangeError('Invalid octet 0x' + w1.toString(16) + ' at offset ' + (i - 1));
        }
        if (i === len) {
            throw new RangeError('Expected additional octet');
        }
        w2 = w[i++];
        if ((w2 & 0xFC00) !== 0xDC00) { // w2 < 0xDC00 || w2 > 0xDFFF)
            throw new RangeError('Invalid octet 0x' + w2.toString(16) + ' at offset ' + (i - 1));
        }
        charCodes.push(((w1 & 0x3ff) << 10) + (w2 & 0x3ff) + 0x10000);
    }
    return String.fromCharCode.apply(String, charCodes);
}

encode Utf16