Node.js Readable Stream data Event

The ‘data’ Event in a Readable Stream is emitted when readable.pipe() and readable.resume() method is called for switching the stream into the flowing mode or by adding a listener callback to the data event. This event can also be emitted by calling readable.read() method and returning the chunk of data available.

Syntax:

Event: 'data'

Below examples illustrate the use of data event in Node.js:

Example 1:

// Node.js program to demonstrate the
// readable data event

// Including fs module
const fs = require('fs');

// Constructing readable stream
const readable = fs.createReadStream("input.txt");

// Instructions to read data
readable.on('readable', () => {
  let chunk;

  // Using while loop and calling
  // read method
  while (null !== (chunk = readable.read())) {

    // Displaying the chunk
    console.log(`read: ${chunk}`);
  }
});

// Handling the data event
readable.on('data', (chunk) => {
  console.log(`chunk length is: ${chunk.length}`);
});

console.log("Done...");

Output:

Done...
chunk length is: 13
read: GeeksforGeeks

Example 2:

// Node.js program to demonstrate the
// readable data event

// Including fs module
const fs = require('fs');

// Constructing readable stream
const readable = fs.createReadStream("input.txt");

// Calling pause method
readable.pause();

// Handling the data event
readable.on('data', (chunk) => {
  console.log(`chunk length is: ${chunk.length}`);
});

console.log("Done...");

Output:

Done...

Reference: https://nodejs.org/api/stream.html#stream_event_data.