Introduction to the `line-reader` Library

The line-reader library is a fundamental tool in the JavaScript ecosystem, particularly for working with Node.js. It enables developers to read files line by line in a memory-efficient way. This is especially critical for handling large files where loading the entire content into memory at once isn’t feasible.

Getting Started with `line-reader`

First, you need to install the `line-reader` library via npm:

 npm install line-reader

Basic Usage

line-reader can be easily set up to read each line of a file in a callback function:

 const lineReader = require('line-reader');
 
 lineReader.eachLine('example.txt', function(line, last) {
   console.log(line);
   if (last) {
     console.log('Finished reading file');
   }
 });

Read Line by Line Synchronously

Although `line-reader` typically operates asynchronously, it also supports synchronous reading:

 const lineReader = require('line-reader');

 lineReader.open('example.txt', function(err, reader) {
   if (err) throw err;

   while (reader.hasNextLine()) {
     reader.nextLine(function(err, line) {
       if (err) throw err;
       console.log(line);
     });
   }

   reader.close(function(err) {
     if (err) throw err;
   });
 });

Handling Lines as Async/Await (Promise Based)

For modern applications, you can utilize the promise-based approach using async/await syntax. However, `line-reader` doesn’t natively support promises, so you might need a wrapper:

 const fs = require('fs');
 const readline = require('readline');

 async function processLineByLine() {
   const fileStream = fs.createReadStream('example.txt');

   const rl = readline.createInterface({
     input: fileStream,
     crlfDelay: Infinity
   });

   for await (const line of rl) {
     console.log(line);
   }
 }

 processLineByLine();

Complete Example – A Line-by-Line File Analyzer

Below is an example of a Node.js application that utilizes `line-reader` to process each line of a file and analyze its content:

 const lineReader = require('line-reader');

 function countWords(line) {
   return line.split(' ').length;
 }

 let totalLines = 0;
 let totalWords = 0;

 lineReader.eachLine('example.txt', function(line, last) {
   totalLines++;
   totalWords += countWords(line);

   console.log(`Line: ${line}`);
   console.log(`Total Words: ${totalWords}`);
   console.log(`Total Lines: ${totalLines}`);

   if (last) {
     console.log('File Analysis Complete');
     console.log('Total Lines:', totalLines);
     console.log('Total Words:', totalWords);
   }
 });

This example demonstrates how you can leverage `line-reader` to read and process files efficiently, making it a versatile choice for Node.js developers.

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