Node js Write a line into a txt file

Question

I want to create a simple Log System  which prints a line before the past line into a txt file by using Node js  but i dont know how the File System from Node js works  Can someone explain it

User · Accepted Answer

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

User · Answer

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

User · Answer

I did a log file which prints data into text file using  Winston  log  The source code is here below   const   createLogger  format  transports     require  winston    var fs   require  fs   var logger   fs createWriteStream  Data Log txt      flags   a      const os   require  os    var sleep   require  system-sleep    var endOfLine   require  os   EOL  var t                   var s               var q                      var array1     var array2     var array3     var array4      array1 0      78   array1 1      56  array1 2      24  array1 3      34   for  var n 0 n lt 4 n      array2 n  array1 n  toString       for  var k 0 k lt 4 k      array3 k  Buffer from                             for  var a 0 a lt 4 a        array4 a  Buffer from array2 a       for  m 0 m lt 4 m      array4 m  copy array3 m  0      logger write  Date  q   logger write  Time   q        logger write  Data 01  t   logger write  Data 02  t    logger write  Data 03  t   logger write  Data 04  t   logger write endOfLine   logger write endOfLine   enter code here enter code here     function mydata          user defined function   logger write datechar s   logger write timechar s   for   n   0  n  lt  4  n       logger write array3 n      logger write endOfLine       for        var now   new Date    var dateFormat   require  dateformat    var date   dateFormat now  isoDate    var time   dateFormat now   h MM ss TT     var datechar   date toString    var timechar   time toString    mydata    sleep 5 1000

User · Answer

Step 1  If you have a small file Read all the file data in to memory  Step 2  Convert file data string into Array  Step 3  Search the array to find a location where you want to insert the text  Step 4  Once you have the location insert your text  yourArray splice index 0  new added test      Step 5  convert your array to string  yourArray join        Step 6  write your file like so  fs createWriteStream yourArray     This is not advised if your file is too big

[node.js] Node.js Write a line into a .txt file

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