Node.js Tutorial - Node.js Streams

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Streams in Node.js are based on events.

All of these stream classes inherit from a base abstract Stream class, which inherits from EventEmitter.

var stream = require('stream'); 
var EventEmitter = require('events').EventEmitter; 

console.log(new stream.Stream() instanceof EventEmitter); // true 
console.log(new stream.Readable({}) instanceof stream.Stream); // true 
console.log(new stream.Writable({}) instanceof stream.Stream); // true 
console.log(new stream.Duplex({}) instanceof stream.Stream); // true 
console.log(new stream.Transform({}) instanceof stream.Stream); // true 

The code above generates the following result.

Pipe

All the streams support a pipe operation that can be done using the pipe member function.

This function is called pipe because it mimics the behavior of the command line pipe operator, for example, cat file.txt | grep yourtest

The fs core module provides utility functions to create readable or writable streams from a file.

The following code shows how to stream a file from the file system to the user console.

var fs = require('fs'); 
// Create readable stream 
var readableStream = fs.createReadStream('./a.js'); 
// Pipe it to stdout 
readableStream.pipe(process.stdout); 

You can also chain multiple streams using pipe.

The following code creates a read stream from a file, pipes it through a zip transform stream, and then pipes it to a writable file stream.

This creates a zip file on the file system.

var fs = require('fs'); 
var gzip = require('zlib').createGzip(); 

var inp = fs.createReadStream('a.js'); 
var out = fs.createWriteStream('a.js.gz'); 

// Pipe chain 
inp.pipe(gzip).pipe(out); 

Streams in Node.js are based on events.

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