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Node.js | Streams

Node.js Streams


Hello folks! welcome back to a new edition of our tutorial on Node.js. In this section of our tutorial on Node.js, we will be studying about Node.js Streams.

Streams are objects that lets you read data from a source or write data to a destination in continuous manner. In Node.js, there are four types of streams -

  • Readable Stream - Stream used for read operations.
  • Writable Stream - Stream used for write operations.
  • Duplex Stream - Stream used for both read and write operations.
  • Transform Stream - A type of duplex stream where the output is computed based on input.

Each type of these streams in Node.js is an EventEmitter instance and throws multiple events at different instances of time. Some of the commonly used events are -

  • data - This event is fired when there is data available for read.
  • end - This event is fired when there is no more data to read.
  • error - This event is fired when there is any error receiving or writing data.
  • finish - This event is fired when all the data has been flushed to underlying system.

This tutorial offers a basic understanding of the commonly used operations on streams.


Reading from a Stream

Create a text file, input.txt with the following contents -

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to teach the world in simple and easy manner!!!!!

Create a js file, main.js using the following code -

var fs = require("fs");
var data = '';

// Create a readable stream
var readerStream = fs.createReadStream('input.txt');

// Set the encoding to be utf8. 
readerStream.setEncoding('UTF8');

// Handle stream events --> data, end, and error
readerStream.on('data', function(chunk) {
   data += chunk;
});

readerStream.on('end',function() {
   console.log(data);
});

readerStream.on('error', function(err) {
   console.log(err.stack);
});

console.log("Program Ended");

Now run the main.js to see the result -

$ node main.js

Output

Verify the output.

Program Ended
WebDesignTutorialz is offering self learning content
to teach the world in simple and easy manner!!!!!

Writing to a Stream

Create a js file, main.js using the following code -

var fs = require("fs");
var data = 'Best Tutorial Platform';

// Create a writable stream
var writerStream = fs.createWriteStream('output.txt');

// Write the data to stream with encoding to be utf8
writerStream.write(data,'UTF8');

// Mark the end of file
writerStream.end();

// Handle stream events --> finish, and error
writerStream.on('finish', function() {
   console.log("Write completed.");
});

writerStream.on('error', function(err) {
   console.log(err.stack);
});

console.log("Program Ended");

Now run the main.js to see the result -

$ node main.js

Output

Verify the output.

Program Ended
Write completed.

Now open output.txt created in your current directory; it should have the following -

Best Tutorial Platform


Piping the Streams

Piping is a technique where we provide the output of one stream as an input to another stream. It is mainly used to get data from a stream and then pass the output to another stream. Piping operations has no limit. Now we'll illustrates a piping example for reading from one file and writing it to another file.

Create a js file, main.js using the following code -

var fs = require("fs");

// Create a readable stream
var readerStream = fs.createReadStream('input.txt');

// Create a writable stream
var writerStream = fs.createWriteStream('output.txt');

// Pipe the read and write operations
// read input.txt and write data to output.txt
readerStream.pipe(writerStream);

console.log("Program Ended");

Now run the main.js to see the result -

$ node main.js

Output

Verify the output.

Program Ended

Open the output.txt created in your current directory; it should have the following -

WebDesignTutorialz is offering self learning content
to teach the world in simple and easy manner!!!!!

Chaining the Streams

Chaining is a process to connect the output of one stream to another stream and then create a chain of several stream operations. It is commonly used with piping operations. Now we will use piping and chaining to first compress a file, afterwards decompress the same file.

Create a js file, main.js using the following code -

var fs = require("fs");
var zlib = require('zlib');

// Compress the file input.txt to input.txt.gz
fs.createReadStream('input.txt')
   .pipe(zlib.createGzip())
   .pipe(fs.createWriteStream('input.txt.gz'));
  
console.log("File Compressed.");

Now run the main.js to see the result -

$ node main.js

Output

Verify the output.

File Compressed.

You will discover that the input.txt has been compressed and it created a file input.txt.gz in the current directory. Now, we will try to decompress the same file via the following code -

var fs = require("fs");
var zlib = require('zlib');

// Decompress the file input.txt.gz to input.txt
fs.createReadStream('input.txt.gz')
   .pipe(zlib.createGunzip())
   .pipe(fs.createWriteStream('input.txt'));
  
console.log("File Decompressed.");

Now run the main.js to see the result -

$ node main.js

Output

Verify the output.

File Decompressed.


Alright guys! This is where we are going to be rounding up for this tutorial. In our next tutorial, we will be studying about Node.js File System.

Feel free to ask your questions where necessary and we will attend to them as soon as possible. If this tutorial was helpful to you, you can use the share button to share this tutorial.

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Thanks for reading and bye for now.

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