toUTF8Array.js

// https://stackoverflow.com/questions/18729405/how-to-convert-utf8-string-to-byte-array

function toUTF8Array(str) {
        var utf8 = [];
        for (var i=0; i < str.length; i++) {
            var charcode = str.charCodeAt(i);
            if (charcode < 0x80) utf8.push(charcode);
            else if (charcode < 0x800) {
                utf8.push(0xc0 | (charcode >> 6), 
                          0x80 | (charcode & 0x3f));
            }
            else if (charcode < 0xd800 || charcode >= 0xe000) {
                utf8.push(0xe0 | (charcode >> 12), 
                          0x80 | ((charcode>>6) & 0x3f), 
                          0x80 | (charcode & 0x3f));
            }
            // surrogate pair
            else {
                i++;
                // UTF-16 encodes 0x10000-0x10FFFF by
                // subtracting 0x10000 and splitting the
                // 20 bits of 0x0-0xFFFFF into two halves
                charcode = 0x10000 + (((charcode & 0x3ff)<<10)
                          | (str.charCodeAt(i) & 0x3ff))
                utf8.push(0xf0 | (charcode >>18), 
                          0x80 | ((charcode>>12) & 0x3f), 
                          0x80 | ((charcode>>6) & 0x3f), 
                          0x80 | (charcode & 0x3f));
            }
        }
        return utf8;
    }