In this article I will highlight the basics of using Node.js streams for web development including:

Version Information

  • Author: Jeff Barczewski
  • Published: August 1st, 2013
  • Tags: nodejs, streams
  • Level: Intermediate
  • Prerequisites: buffers, events
  • Node.js v0.10+ (latest stable is v0.10.15 as of this writing), but streams have generally been a part of Node.js from its early days

Opening streams using Node.js core methods

Node.js has a variety of built-in core methods which create readable and writable streams.

Opening a read stream to an existing file

var fs = require('fs');  // file system
var rstream = fs.createReadStream('existingFile');

Opening a write stream for storing data in a file

var fs = require('fs');  // file system
var wstream = fs.createWriteStream('fileToWrite');

Using streams from http

var http = require('http');
var server = http.createServer(function (req, res) {
  // req - request readable stream
  // res - response writable stream
});
server.listen(8000, '127.0.0.1');  // start

Piping streams

Piping streams is taking the output of one stream and feeding it into the input of another.

stream-read-write graphic

Reading from one file and writing to another

var fs = require('fs');  // file system
var rstream = fs.createReadStream('existingFile');
var wstream = fs.createWriteStream('myFileToWriteTo');
rstream.pipe(wstream);

Reading from a file and serving it as response to http request

var fs = require('fs');  // file system
var http = require('http');
var server = http.createServer(function (req, res) {
  // logic here to determine what file, etc
  var rstream = fs.createReadStream('existFile');
  rstream.pipe(res);
});
server.listen(8000, '127.0.0.1');  // start

Listening to stream events

Node.js streams are event emitters so you can listen to its events to monitor the data being transmitted.

Listening to data events to determine the size

var dataLength = 0;
// using a readStream that we created already
rstream
  .on('data', function (chunk) {
    dataLength += chunk.length;
  })
  .on('end', function () {  // done
    console.log('The length was:', dataLength);
  });

Using streams created by Node.js core modules, the data type for chunk will usually be a Buffer or a string, both of which implement the length method.

Streams are powerful but easy to use

With these basics you can begin to use the power of Node.js streams in your programs. In future articles I will build on this to showcase more advanced features of streams.

If you enjoyed this article or have any questions, please leave a comment or contact me via email or social network.

For additional reading