Node.js Write a line into a .txt file

Question

I want to use Node.js to create a simple logging system which prints a line before the past line into a .txt file. However, I don't know how the file system functionality from Node.js works.

Can someone explain it?

Answer 1

Simply use fs module and something like this:

fs.appendFile('server.log', 'string to append', function (err) {    if (err) return console.log(err);    console.log('Appended!'); }); 

Answer 2

Inserting data into the middle of a text file is not a simple task. If possible, you should append it to the end of your file.

The easiest way to append data some text file is to use build-in fs.appendFile(filename, data[, options], callback) function from fs module:

var fs = require('fs') fs.appendFile('log.txt', 'new data', function (err) {   if (err) {     // append failed   } else {     // done   } }) 

But if you want to write data to log file several times, then it'll be best to use fs.createWriteStream(path[, options]) function instead:

var fs = require('fs') var logger = fs.createWriteStream('log.txt', {   flags: 'a' // 'a' means appending (old data will be preserved) })  logger.write('some data') // append string to your file logger.write('more data') // again logger.write('and more') // again 

Node will keep appending new data to your file every time you'll call .write, until your application will be closed, or until you'll manually close the stream calling .end:

logger.end() // close string 

Note that logger.write in the above example does not write to a new line. To write data to a new line:

var writeLine = (line) => logger.write(`\n${line}`); writeLine('Data written to a new line');