custom-writable-stream.js

custom-writable-stream.js

// example from http://codewinds.com/blog/2013-08-19-nodejs-writable-streams.html
"use strict";

var stream = require('stream');
var util = require('util');
// use Node.js Writable, otherwise load polyfill
var Writable = stream.Writable;

var memStore = { };

/* Writable memory stream */
function WMStrm(key, options) {
  // allow use without new operator
  if (!(this instanceof WMStrm)) {
    return new WMStrm(key, options);
  }
  Writable.call(this, options); // init super
  this.key = key; // save key
  memStore[key] = new Buffer(''); // empty
}
util.inherits(WMStrm, Writable);

WMStrm.prototype._write = function (chunk, enc, cb) {
  // our memory store stores things in buffers
  var buffer = (Buffer.isBuffer(chunk)) ?
    chunk :  // already is Buffer use it
    new Buffer(chunk, enc);  // string, convert

  // concat to the buffer already there
  memStore[this.key] = Buffer.concat([memStore[this.key], buffer]);
  cb();
};


// Trying our stream out
var wstream = new WMStrm('foo');

wstream.on('finish', function () {
  console.log('finished writing');
  console.log('value is:', memStore.foo.toString());
});

wstream.write('hello ');
wstream.write('world');
wstream.end();