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  • Use of Streams in NodeJs

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    Streams are objects, which are use to read/write operation from or to a file. There are four types of streams.

    Readable -  used for read file. Writable -used for write file.

    Duplex - used for both read and write a file.

    Transform – Its type of duplex stream where the output is computed based on input.

    The stream is an EventEmitter instance and triggers several events at a different instance of times.

     

    These events like data, end, error, finish which commonly used.

    data - Triggered when there is data is available to read.

    end - Triggered when there is no more data to read.

    error - Triggered when there is any error receiving.

    finish - Triggered when all data has been flushed to the underlying system.

    These above operations are commonly used on NodeJs stream.

     

     

    Readable Stream example:

    let's create a js file named test.js as below:

    var fs = require("fs");
    var data = '';
    //readable stream
    var readerStream = fs.createReadStream('test.txt');
    //encoding to utf8. 
    readerStream.setEncoding('UTF8');
    // Handle stream events i.e.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 is Ended");

     

    And another file as test.txt like

    Data Intensive Real time Applications (DIRT)
    Data Streaming Applications
    JSON APIs based Applications
    Single Page Applications

     

    Now run the test.js on NodeJs.REPL by command:

    $ nodejs test.js

    The Output is :

    Program is Ended
    Data Intensive Real time Applications (DIRT)
    Data Streaming Applications
    JSON APIs based Applications
    Single Page Applications

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