code: function UTF16Encoder(utf16_be, options) {
      var fatal = options.fatal;
      /**
       * @param {Stream} stream Input stream.
       * @param {number} code_point Next code point read from the stream.
       * @return {(number|!Array.<number>)} Byte(s) to emit.
       */
      this.handler = function(stream, code_point) {
        // 1. If code point is end-of-stream, return finished.
        if (code_point === end_of_stream)
          return finished;
  
        // 2. If code point is in the range U+0000 to U+FFFF, return the
        // sequence resulting of converting code point to bytes using
        // utf-16be encoder flag.
        if (inRange(code_point, 0x0000, 0xFFFF))
          return convertCodeUnitToBytes(code_point, utf16_be);
  
        // 3. Let lead be ((code point − 0x10000) >> 10) + 0xD800,
        // converted to bytes using utf-16be encoder flag.
        var lead = convertCodeUnitToBytes(
          ((code_point - 0x10000) >> 10) + 0xD800, utf16_be);
  
        // 4. Let trail be ((code point − 0x10000) & 0x3FF) + 0xDC00,
        // converted to bytes using utf-16be encoder flag.
        var trail = convertCodeUnitToBytes(
          ((code_point - 0x10000) & 0x3FF) + 0xDC00, utf16_be);
  
        // 5. Return a byte sequence of lead followed by trail.
        return lead.concat(trail);
      };
    }
docs: 15.2.2 shared utf-16 encoder 
  @constructor
  @implements {Encoder}
  @param {boolean} utf16_be True if big-endian, false if little-endian.
  @param {{fatal: boolean}} options