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..." );
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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..." );
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Output:
Done...
Reference: https://nodejs.org/api/stream.html#stream_event_data.