Node Streams (through and though2)

testStreams.js

var through2 = require('through2');
var through = require('through');
var fs = require('fs');

//This is what most people use
fs.createReadStream('testStreams.js')
  .pipe(through2(function(chunk, enc, cb) {
  	console.log('t2', 's1');
  	cb(null, chunk);
  }, function(cb) {
  	console.log('t2', 'e1');
  	cb();
  }))
  .pipe(through2(function(chunk, enc, cb) {
  	console.log('t2', 's2');
  	//Since I don't call back with the chunk, no data is streamed to the next one!
  	//s3 is never fired!
  	cb();
  }, function(cb) {
  	console.log('t2', 'e2');
  	//Since I don't cb, e3 is never fired!
  	//cb();
  }))
  .pipe(through2(function(chunk, enc, cb) {
  	console.log('t2', 's3');
  	cb();
  }, function(cb) {
  	console.log('t2', 'e3');
  	cb();
  }));

//This is what mold-source-map uses
fs.createReadStream('testStreams.js')
  .pipe(through(function(data) {
  	console.log('t1', 's1');
  	//s2 only fires if data is queued here
  	this.queue(data);
  }, function() {
  	console.log('t1', 'e1');
  	//e2 only fires if end is emitted here
  	this.emit('end');
  }))
  .pipe(through(function(data) {
  	console.log('t1', 's2');
  	//s3 is not fired because data is NOT queued here
  }, function() {
  	console.log('t1', 'e2');
  	//e3 is not fired next end is NOT emitted here
  	fs.writeFile('test.test', 'test', 'utf8', function(err) {
  	  console.log(err);
  	  //However, this will pass data and trigger s3
    	this.queue('blue');
    	//and this should trigger e3
    	this.queue(null);
    }.bind(this));
  }))
  .pipe(through(function(data) {
  	console.log('t1', 's3');
  }, function() {
  	console.log('t1', 'e3');
  }));