Comprehensive Guide to Line Reader Node.js Module and Its Extensive APIs

Welcome to our comprehensive guide on the line-reader module for Node.js! This powerful utility makes it quick and efficient to read through lines in a file without loading the entire file into memory. Whether you’re parsing logs, analyzing data, or processing large files, line-reader has you covered.

Getting Started with Line Reader

To install the line-reader library, you can use npm:

npm install line-reader

Basic Usage

Here is a simple example of reading a file line by line:

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

Advanced Usage and API Examples

Reading Lines Synchronously

Sometimes you may want to read lines synchronously. Use eachLineSync for this purpose:

 const lineReader = require('line-reader');
lineReader.eachLineSync('file.txt', function(line) {
  console.log(line);
}); 

Reading with a Stream

Using a stream can be more efficient for large files:

 const lineReader = require('line-reader'); const fs = require('fs');
const stream = fs.createReadStream('file.txt'); lineReader.open(stream, function(reader) {
  reader.nextLine(function(err, line) {
    while (line) {
      console.log(line);
      reader.nextLine(callback);
    }
  });
}); 

Skipping Lines

You can also skip lines by returning false in the callback:

 const lineReader = require('line-reader');
lineReader.eachLine('file.txt', function(line) {
  if (line.includes('skip')) {
    return false;
  }
  console.log(line);
}); 

Building a Sample App with Line Reader

Let’s build a simple Node.js application that processes a large CSV file and filters out rows based on a condition:

 const lineReader = require('line-reader'); const fs = require('fs');
const output = fs.createWriteStream('filtered.csv'); output.write('Name,Age,Occupation\n'); // header for the new CSV
lineReader.eachLine('data.csv', function(line, last) {
  const columns = line.split(',');
  if (columns[1] > 30) {
    output.write(line + '\n');
  }
  if (last) {
    output.end();
    console.log('Finished processing CSV');
  }
}); 

This app reads through a CSV file and writes rows where the age is greater than 30 to a new file.

Conclusion

The line-reader library offers a robust set of APIs for reading lines from files efficiently. Whether you need to deal with giant log files or small config files, line-reader is a great tool in your Node.js toolkit.

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