notes/node_modules/duplexer2/index.js

var stream = require("readable-stream");

var duplex2 = module.exports = function duplex2(options, writable, readable) {
  return new DuplexWrapper(options, writable, readable);
};

var DuplexWrapper = exports.DuplexWrapper = function DuplexWrapper(options, writable, readable) {
  if (typeof readable === "undefined") {
    readable = writable;
    writable = options;
    options = null;
  }

  options = options || {};
  options.objectMode = true;

  stream.Duplex.call(this, options);

  this._bubbleErrors = (typeof options.bubbleErrors === "undefined") || !!options.bubbleErrors;

  this._writable = writable;
  this._readable = readable;

  var self = this;

  writable.once("finish", function() {
    self.end();
  });

  this.once("finish", function() {
    writable.end();
  });

  readable.on("data", function(e) {
    if (!self.push(e)) {
      readable.pause();
    }
  });

  readable.once("end", function() {
    return self.push(null);
  });

  if (this._bubbleErrors) {
    writable.on("error", function(err) {
      return self.emit("error", err);
    });

    readable.on("error", function(err) {
      return self.emit("error", err);
    });
  }
};
DuplexWrapper.prototype = Object.create(stream.Duplex.prototype, {constructor: {value: DuplexWrapper}});

DuplexWrapper.prototype._write = function _write(input, encoding, done) {
  this._writable.write(input, encoding, done);
};

DuplexWrapper.prototype._read = function _read(n) {
  this._readable.resume();
};