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Explain types of streams in Node.js?

Answer»

Streams are abstract interface available with Node.js.The stream module HELPS in implementation of streaming data. There are four TYPES of streams.

  • <Readable> for the reading operation
  • <Writable> for the writing operation
  • <Duplex> for both reading and writing operations
  • <Transform> is a derived from Duplex stream that computes available input.

The important events on a readable stream are:

  • The data EVENT, where the stream passes a chunk of data to the consumer.
  • The end event, which happens when there is no more data to be used from the stream.

For eg:

Reading a file “input.txt”

var fs = require('fs'); var readableStream = fs.createReadStream('input.txt'); // creates readable stream                  var data = ''; readableStream.on('data', function(txt) {    // data event produces the flow of data     data+=txt; }); readableStream.on('end', function()  // end event is triggered when no data to read {     console.log(data); });

The important events on a writable stream are:

  • The write event, that signals that the writable stream can receive more data.
  • The finish event, that is produced when all data has been written to the underlying system.

For eg:

Write “Hello World “ to file.txt

var fs = require("fs"); var data = 'Hello world'; var writerStream = fs.createWriteStream('file.txt');  // Create a writable stream writerStream.write(data,'UTF8'); // Write the data to stream  // Mark the end of file writerStream.end(); writerStream.on('finish', function() {  // finish triggered when all data is written to     console.log("Write completed."); });

PIPING the streams is one of the most popular mechanisms in Node.js programs where output of one stream is provided as the input to another stream.For eg:

var fs = require("fs"); var readerStream = fs.createReadStream('example.txt'); // Readable stream var writerStream = fs.createWriteStream('exampleOutput.txt'); // Writable stream readerStream.pipe(writerStream);// Pipe the readable stream as input to writable stream console.log("Program Ended");


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