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How Can I Efficiently Read a Large Text File Line by Line in Node.js?
How Can I Efficiently Read a Large Text File Line by Line in Node.js?
Dec 07, 2024 am 02:35 AM
Reading Text Files Line-by-Line in Node.js
reading a large text file one line at a time in Node.js can be a crucial operation for processing extensive datasets. While the question you mentioned from Quora tackles reading from STDIN, this article focuses on extending this concept to reading from a text file.
The initial approach, involving fs.open, serves as a foundation. The missing step is to leverage the Lazy module to perform line-by-line reading from the opened filedescriptor. However, since Node.js v0.12, there is a more robust solution using the built-in readline core module.
Let's explore two approaches using readline:
const fs = require('fs');
const readline = require('readline');
async function processLineByLine() {
const fileStream = fs.createReadStream('input.txt');
const rl = readline.createInterface({
input: fileStream,
crlfDelay: Infinity
});
// Note: we use the crlfDelay option to recognize all instances of CR LF
// ('\r\n') in input.txt as a single line break.
for await (const line of rl) {
// Each line in input.txt will be successively available here as `line`.
console.log(`Line from file: ${line}`);
}
}
processLineByLine();
Alternatively, you can use:
var lineReader = require('readline').createInterface({
input: require('fs').createReadStream('file.in')
});
lineReader.on('line', function (line) {
console.log('Line from file:', line);
});
lineReader.on('close', function () {
console.log('all done, son');
});
Both approaches leverage the readline module to effectively read lines from a text file one at a time. The last line is read correctly (as of Node v0.12 or later), even if there is no final line break.
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