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const fs = require('fs');
const readStream = fs.createReadStream('largeFile.txt');
readStream.on('data', (chunk) => {
// process the chunk of data
});
readStream.on('end', () => {
// done reading file
});
readStream.on('error', (err) => {
// handle error
});
In this example, the ‘data’ event is emitted each time a new chunk of data is available. The size of each chunk can be configured by passing an optional ‘highWaterMark’ parameter to the ‘createReadStream’ method.
When writing large files, we can use the ‘createWriteStream’ method to write data in chunks:
const fs = require('fs');
const writeStream = fs.createWriteStream('largeFile.txt');
writeStream.write('some data');
// write more data in chunks
writeStream.write('more data');
writeStream.write('even more data');
writeStream.end();
In this example, the ‘write’ method is used to write data in chunks, and the ‘end’ method is called to signal the end of the write operation.
By using streams to process large files, we can avoid loading the entire file into memory at once and instead work with the file data in smaller, more manageable chunks. This can help to optimize memory usage and improve the performance of our Node.js applications.
const fs = require('fs');
const csv = require('csv-parser');
// Read data from CSV file
fs.createReadStream('data.csv')
.pipe(csv())
.on('data', (data) => {
// Process each row of data
console.log(data);
})
.on('end', () => {
console.log('CSV file successfully processed');
});
In this example, we first require the fs and csv-parser modules. We then create a readable stream from the data.csv file using the createReadStream() method provided by the fs module.
We pipe the contents of this stream through the csv() function provided by the csv-parser module, which converts each row of the CSV file into a JavaScript object.
We then listen for the data event, which is emitted each time a new row is read from the CSV file. In the event handler, we process each row of data as needed (in this example, we simply log it to the console).
Finally, we listen for the end event, which is emitted when all rows have been processed. In this case, we log a message indicating that the CSV file has been successfully processed.
const buffer = Buffer.from('hello world');
const str = buffer.toString('utf8');
console.log(str); // output: 'hello world'
To convert a string to a buffer, you can use the Buffer.from() method, which takes the string as the first parameter and an optional encoding as the second parameter. For example:
const str = 'hello world';
const buffer = Buffer.from(str, 'utf8');
console.log(buffer); // output: <Buffer 68 65 6c 6c 6f 20 77 6f 72 6c 64>
Note that the default encoding for toString() and Buffer.from() is 'utf8', but you can specify a different encoding if needed.
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