Node log in a file instead of the console

Question

Can I configure console log so that the logs are written on a file instead of being printed in the console

User · Answer

I often use many arguments to console log   and console error    so my solution would be   var fs   require  fs    var util   require  util    var logFile   fs createWriteStream  log txt     flags   a           Or  w  to truncate the file every time the process starts  var logStdout   process stdout   console log   function        logFile write util format apply null  arguments      n      logStdout write util format apply null  arguments      n      console error   console log

User · Answer

I took on the idea of swapping the output stream to a my stream   const LogLater                  require     loglater js    var logfile new LogLater   log    new Date   toISOString   replace    a-zA-Z0-9  g  -       txt       var PassThrough   require  stream   PassThrough   var myout  new PassThrough    var wasout console  stdout  myout on  data   data   gt  logfile dateline   r n  data  wasout write data      console  stdout myout   var myerr  new PassThrough    var waserr console  stderr  myerr on  data   data   gt  logfile dateline   r n  data  waserr write data      console  stderr myerr    loglater js   const fs   require  fs     function LogLater filename  noduplicates  interval        this filename   filename     loglater txt       this arr           this timeout   false      this interval   interval    1000      this noduplicates   noduplicates    true      this onsavetimeout bind   this onsavetimeout bind this       this lasttext           process on  exit      gt   if this timeout clearTimeout this timeout  this timeout false  this save          LogLater prototype          log  function  log text            this arr push text           if   this timeout  this timeout   setTimeout this onsavetimeout bind  this interval              text  function log text  loglastline            if  this noduplicates                if  this lasttext     text  return              this lastline   text                    this  log text              line  function log text  loglastline            if  this noduplicates                if  this lasttext     text  return              this lastline   text                    this  log text     r n               dateline  function dateline text            if  this noduplicates                if  this lasttext     text  return              this lastline   text                    this  log   new Date    toISOString        t    text     r n               onsavetimeout  function onsavetimeout             this timeout   false          this save               save  function save     fs appendFile this filename  this arr splice 0  this arr length  join      function err    if  err  console log err stack           module exports   LogLater

User · Answer

Winston is a very-popular npm-module used for logging     Here is a how-to  Install winston in your project as   npm install winston --save   Here s a configuration ready to use out-of-box that I use frequently in my projects as logger js under utils           Configurations of logger      const winston   require  winston    const winstonRotator   require  winston-daily-rotate-file     const consoleConfig       new winston transports Console        colorize   true          const createLogger   new winston Logger      transports   consoleConfig      const successLogger   createLogger  successLogger add winstonRotator       name    access-file      level    info      filename      logs access log      json   false     datePattern    yyyy-MM-dd-      prepend   true      const errorLogger   createLogger  errorLogger add winstonRotator       name    error-file      level    error      filename      logs error log      json   false     datePattern    yyyy-MM-dd-      prepend   true      module exports        successlog   successLogger     errorlog   errorLogger      And then simply import wherever required as this   const errorLog   require     util logger   errorlog  const successlog   require     util logger   successlog    Then you can log the success as   successlog info  Success Message and variables    variable       and Errors as   errorlog error  Error Message     error       It also logs all the success-logs and error-logs in a file under logs directory date-wise as you can see here

User · Answer

Another solution not mentioned yet is by hooking the Writable streams in process stdout and process stderr  This way you don t need to override all the console functions that output to stdout and stderr  This implementation redirects both stdout and stderr to a log file   var log file   require  fs   createWriteStream   dirname     log txt    flags    w     function hook stream stream  callback        var old write   stream write      stream write    function write            return function string  encoding  fd                write apply stream  arguments      comments this line if you don t want output in the console             callback string  encoding  fd                   stream write       return function             stream write   old write          console log  a   console error  b    var unhook stdout   hook stream process stdout  function string  encoding  fd        log file write string  encoding      var unhook stderr   hook stream process stderr  function string  encoding  fd        log file write string  encoding      console log  c   console error  d    unhook stdout   unhook stderr    console log  e   console error  f     It should print in the console  a b c d e f   and in the log file   c d   For more info  check this gist

User · Answer

Straight from nodejs s API docs on Console  const output   fs createWriteStream    stdout log    const errorOutput   fs createWriteStream    stderr log       custom simple logger const logger   new Console output  errorOutput      use it like console const count   5  logger log  count   d   count      in stdout log  count 5

User · Answer

const fs   require  fs    const  keys    Object  const  Console    console          Redirect console to a file   Call without path or with false-y    value to restore original behavior      param  string   path      function file path        const con   path   new Console fs createWriteStream path     null       keys Console prototype  forEach key   gt            if  path                this key        args    gt  con key     args             else               delete this key                            patch global console object and export module exports   console file   file    To use it  do something like   require    console-file    console file   path to log    console log  write to file     console error  also write to file     console file          go back to writing to stdout

User · Answer

I just build a pack to do this  hope you like it    https   www npmjs com package writelog

User · Answer

For simple cases  we could redirect the Standard Out  STDOUT  and Standard Error  STDERR  streams directly to a file say  test log  using   gt   and  2 gt  amp 1  Example     test js  function            Below outputs are sent to Standard Out  STDOUT  stream     console log  quot Hello Log quot        console info  quot Hello Info quot           Below outputs are sent to Standard Error  STDERR  stream     console error  quot Hello Error quot        console warn  quot Hello Warning quot            node test js  gt  test log 2 gt  amp 1  As per the POSIX standard   input    output  and  error  streams are identified by the positive integer file descriptors  0  1  2   i e   stdin is 0  stdout is 1  and stderr is 2   Step 1   2 gt  amp 1  will redirect from 2  stderr  to 1  stdout  Step 2    gt   will redirect from  1  stdout  to file  test log

User · Answer

Overwriting console log is the way to go  But for it to work in required modules  you also need to export it   module exports   console    To save yourself the trouble of writing log files  rotating and stuff  you might consider using a simple logger module like winston      Include the logger module var winston   require  winston       Set up log file   you can also define size  rotation etc   winston add winston transports File    filename   somefile log         Overwrite some of the build-in console functions console error   winston error  console log   winston info  console info   winston info  console debug   winston debug  console warn   winston warn  module exports   console

User · Answer

If this is for an application  you re probably better off using a logging module  It ll give you more flexibility  Some suggestions    winston https   github com indexzero winston log4js https   github com nomiddlename log4js-node

User · Answer

You can now use Caterpillar which is a streams based logging system  allowing you to log to it  then pipe the output off to different transforms and locations   Outputting to a file is as easy as   var logger   new  require       Logger     logger pipe require  fs   createWriteStream    debug log     logger log  your log message      Complete example on the Caterpillar Website

User · Answer

For future users   keshavDulal answer doesn t work for latest version  And I couldn t find a proper fix for the issues that are reporting in the latest version 3 3 3  Anyway I finally fixed it after researching a bit  Here is the solution for winston version 3 3 3 Install winston and winston-daily-rotate-file npm install winston  npm install winston-daily-rotate-file  Create a new file utils logger js const winston   require  winston    const winstonRotator   require  winston-daily-rotate-file     var logger   new winston createLogger     transports        new  winston transports DailyRotateFile          name   access-file         level   info         filename     logs access log         json  false        datePattern   yyyy-MM-DD         prepend  true        maxFiles  10             new  winston transports DailyRotateFile          name   error-file         level   error         filename     logs error log         json  false        datePattern   yyyy-MM-DD         prepend  true        maxFiles  10                  module exports       logger     Then in  any file where you want to use logging import the module like const logger   require    utils logger   logger   Use logger like the following  logger info  Info service started    logger error  Service crashed

User · Answer

You can also have a look at this  npm module  https   www npmjs com package noogger  noogger  simple and straight forward

User · Answer

I for myself simply took the example from winston and added the log      method  because winston names it info       Console js     use strict      Include the logger module const winston   require  winston     const logger   winston createLogger       level   info       format  winston format json        transports                          - Write to all logs with level  info  and below to  combined log             - Write all logs error  and below  to  error log                      new winston transports File   filename   error log   level   error              new winston transports File   filename   combined log                      If we re not in production then log to the  console  with the format        info level     info message  JSON stringify      rest         if  process env NODE ENV      production         logger add new winston transports Console           format  winston format simple                  Add log command logger log logger info   module exports   logger    Then simply use in your code    const console   require  Console     Now you can simply use the normal log functions in your file and it will create a file AND log it to your console  while debugging developing   Because of if  process env NODE ENV      production      in case you want it also in production

User · Answer

METHOD STDOUT AND STDERR  This approach can help you  I use something similar in my projects  and works for all methods including console log  console warn  console error  console info  This method write the bytes written in stdout and stderr to file  Is better than changing console log  console warn  console error  console info methods  because output will be exact the same as this methods output   var fs  require  fs   var os  require  os   var HOME  os homedir   var stdout r   fs createWriteStream HOME     node stdout log     flags   a     var stderr r   fs createWriteStream HOME     node stderr log     flags   a      var attachToLog  function std  std new        var originalwrite  std write     std write  function data enc           try              var d  data             if  Buffer isBuffer d                   d  Buffer from data   typeof enc      string     enc    utf8               std new write apply std new  d           catch e            return originalwrite apply std  arguments            attachToLog process stdout  stdout r  attachToLog process stderr  stderr r      recommended catch error on stdout r and stderr r    stdout r on  error   yourfunction     stderr r on  error   yourfunction

User · Answer

You could also just overload the default console log function   var fs   require  fs    var util   require  util    var log file   fs createWriteStream   dirname     debug log    flags    w     var log stdout   process stdout   console log   function d         log file write util format d      n      log stdout write util format d      n         Above example will log to debug log and stdout   Edit  See multiparameter version by Cl  ment also on this page

User · Answer

Improve on Andres Riofrio   to handle any number of arguments  var fs   require  fs    var util   require  util     var log file   fs createWriteStream   dirname     debug log    flags    w     var log stdout   process stdout   console log   function    args        var output   args join           log file write util format output      r n        log stdout write util format output      r n

User · Answer

Update 2013 - This was written around Node v0 2 and v0 4  There are much better utilites now around logging  I highly recommend Winston  Update Late 2013 - We still use winston  but now with a logger library to wrap the functionality around logging of custom objects and formatting  Here is a sample of our logger js https   gist github com rtgibbons 7354879    Should be as simple as this     var access   fs createWriteStream dir     node access log     flags   a             error   fs createWriteStream dir     node error log     flags   a          redirect stdout   stderr proc stdout pipe access   proc stderr pipe error

User · Answer

If you are looking for something in production winston is probably the best choice   If you just want to do dev stuff quickly  output directly to a file  I think this works only for  nix systems    nohup node simple-server js  gt  output log  amp

[node.js] Node: log in a file instead of the console

Examples related to node.js