decode_emoji.js

function displayEmoji() {

  /**
   * utf8ByteArrayToString() copied from:
   *   https://github.com/google/closure-library/blob/e877b1eac410c0d842bcda118689759512e0e26f/closure/goog/crypt/crypt.js
   *
   * Converts a UTF-8 byte array to JavaScript's 16-bit Unicode.
   * @param {Uint8Array|Array<number>} bytes UTF-8 byte array.
   * @return {string} 16-bit Unicode string.
   */
  var utf8ByteArrayToString = function(bytes) {
    var out = [], pos = 0, c = 0;
    while (pos < bytes.length) {
      var c1 = bytes[pos++];
      if (c1 < 128) {
        out[c++] = String.fromCharCode(c1);
      } else if (c1 > 191 && c1 < 224) {
        var c2 = bytes[pos++];
        out[c++] = String.fromCharCode((c1 & 31) << 6 | c2 & 63);
      } else if (c1 > 239 && c1 < 365) {
        // Surrogate Pair
        var c2 = bytes[pos++];
        var c3 = bytes[pos++];
        var c4 = bytes[pos++];
        var u = ((c1 & 7) << 18 | (c2 & 63) << 12 | (c3 & 63) << 6 | c4 & 63) -
                0x10000;
        out[c++] = String.fromCharCode(0xD800 + (u >> 10));
        out[c++] = String.fromCharCode(0xDC00 + (u & 1023));
      } else {
        var c2 = bytes[pos++];
        var c3 = bytes[pos++];
        out[c++] =
          String.fromCharCode((c1 & 15) << 12 | (c2 & 63) << 6 | c3 & 63);
      }
    }
    return out.join('');
  }

  jQuery(this).text(utf8ByteArrayToString(JSON.parse(jQuery(this).attr('data-emoji-bytes'))));
}