// From string to bytes:
var bytes = utf8.stringToUTF8Bytes('hello utf8 € $');
// bytes = [104,101,108,108,111,32,117,116,102,56,32,226,130,172,32,36];
// From bytes to string:
var str = utf8.UTF8BytesToString(bytes)
// str = 'hello utf8 € $'

/**
 * Convert string to UTF8 byte sequence.
 * @param {string} str javascript string (unicode).
 * @return {Array.<number>} byte sequence.
 */
function stringToUTF8Bytes (str) {}

/**
 * Convert UTF8 byte sequence to string.
 * @param {Array.<number>} bytes UTF8 byte sequence.
 * @return {?string} result string or null on error (invalid input).
 */
function UTF8BytesToString(bytes) {}