Can I configure console.log so that the logs are written on a file instead of being printed in the console?
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 Clément also on this page.
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);
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 > output.log &
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;
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.
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 => {
if (path) {
this[key] = (...args) => 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
For simple cases, we could redirect the Standard Out (STDOUT) and Standard Error (STDERR) streams directly to a file(say, test.log) using '>' and '2>&1'
Example:
// test.js
(function() {
// Below outputs are sent to Standard Out (STDOUT) stream
console.log("Hello Log");
console.info("Hello Info");
// Below outputs are sent to Standard Error (STDERR) stream
console.error("Hello Error");
console.warn("Hello Warning");
})();
node test.js > test.log 2>&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>&1' will redirect from 2 (stderr) to 1 (stdout)
Step 2: '>' will redirect from 1 (stdout) to file (test.log)
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/winstonjs/winston
log4js https://github.com/nomiddlename/log4js-node
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
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.
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;
If you're using linux, you can also use output redirection. Not sure about Windows.
node server.js >> file.log 2>> file.log
>> file.log to redirect stdout to the file
2>> file.log to redirect stderr to the file
others use the shorthand &>> for both stdout and stderr but it's not accepted by both my mac and ubuntu :(
extra: > overwrites, while >> appends.
By the way, regarding NodeJS loggers, I use pino + pino-pretty logger
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)
Adding to the answer above, a lit bit of an expansion to the short and efficient code overriding console.log. Minor additions: set filename with date, wrapper function, also do the original console.logging to keep the console active with the info.
Usage: in the beginning of your code, run setConsoleLogToFile([FILENAME]).
const fs = require("fs"),
util = require('util');
const getPrettyDate = ()=> new Date().toString().replace(":","-").replace(/00\s\(.*\)/, "").replace(` ${new Date().getFullYear()}`, ",").replace(/:\d\d\s/, " ");
module.exports.getPrettyDate = getPrettyDate;
module.exports.setConsoleLogToFile = (filename) => {
const log_file = fs.createWriteStream(`${__dirname}/${filename} - ${getPrettyDate()}.log`, { flags: 'w' }),
log_stdout = process.stdout;
const origConsole = console.log;
console.log = (d) => {
origConsole(d);
log_file.write(util.format(d) + '\n');
log_stdout.write(util.format(d) + '\n');
};
}
Most logger is overkill and does not support the build in console.log correctly. Hence I create console-log-to-file:
import { consoleLogToFile } from "console-log-to-file";
// or `const { consoleLogToFile } = require("console-log-to-file/dist/index.cjs.js")`
consoleLogToFile({
logFilePath: "/log/default.log",
});
// all of your console.log/warn/error/info will work as it does and save to file now.
If you are looking for a solution without modifying any code, here is a simple solution.
It requires pm2, just add it to your node modules and start you app with
pm2 start server.js
And you are done, console.logs are now automatically registered under home/.pm2/logs/server-out.log.
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');
};
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
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');
if you are using forever to keep your node app running, then typing forever list will show you the path to the log file that console.log is writing too
You can use the nodejs Console constructor
const mylog = new console.Console(
fs.createWriteStream("log/logger.log"),
fs.createWriteStream("log/error.log")
);
And then you can use it just like the normal console class, eg:
mylog.log("Ok!"); // Will be written into 'log/logger.log'
mylog.error("Bad!"); // Will be written into 'log/error.log'
You can also have a look at this npm module:
https://www.npmjs.com/package/noogger
noogger
simple and straight forward...
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)=>{logfile.dateline("\r\n"+data);wasout.write(data);});
console._stdout=myout;
var myerr= new PassThrough();
var waserr=console._stderr;
myerr.on('data',(data)=>{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',()=>{ 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;
I just build a pack to do this, hope you like it ;)
https://www.npmjs.com/package/writelog
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)...
Create a utils/logger.js file with:
var fs = require('fs');
var util = require('util');
var log_file = fs.createWriteStream(__dirname + '/../logs/server.log', { flags: 'w' });
var log_stdout = process.stdout;
console.log = function () { //
[...arguments].forEach(element => {
log_file.write(util.format(element) + '\n');
log_stdout.write(util.format(element) + '\n');
});
};
module.exports = {
console
}
Include the logger.js file from any file where you want to console.log like:
const console = require('./utils/logger').console;
Create a logs folder and create an empty server.log file in it and run your app :)
Rudy Huynh's solution worked really well for me. I added a little bit to have it spit out files with today's date and time.
var dateNow = new Date();
var timeNow = dateNow.getHours() + '-' + dateNow.getMinutes();
var logPath = "log/" + dateNow.toDateString() + ' -' + ' Start Time - ' + timeNow + ".log"
consoleLogToFile({
logFilePath: logPath
});
It's not very elegant but this way it'll save different, easy to read, log files instead of just updating the same "default.log" file.
Based on multiparameter version by Clément, just without color codes for the text file
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 () {
// Storing without color codes
logFile.write(util.format.apply(null,arguments).replace(/\033\[[0-9;]*m/g,"") + '\n');
// Display normally, with colors to Stdout
logStdout.write(util.format.apply(null, arguments) + '\n');
}
Note: Answering since I couldn't comment
So I've been working with Node.js on C9 recently and ran into this problem in a javascript file:
jsdom.env("", function(err, window) {
TypeError: jsdom.env is not a function
Here is my code:
var jsdom = require('jsdom');
var $;
jsdom.env("", function(err, window) {
console.log("what");
if (err) {
console.error(err);
return;
}
$ = require("jquery")(window);
$.ajax(settings).done(function (response) {
console.log(response);
});
});
I updated all my dependencies as well as Node itself but still get this problem. Does anyone know what's up?
I was facing the same issue. Was looking for the solution all over the web. It turned out that jsdom has updated some of their features since v10. So, I wanted to use jQuery in the Node.js end of an express app.
For those who are just looking for answers about how to include jQuery in Node, I would like to mention that you'll need to install jsdom using npm install jsdom and jQuery using npm install jquery. Then:
For jQuery to work in Node, a window with a document is required. Since no such window exists natively in Node, one can be mocked by jsdom as below:
var jsdom = require('jsdom');
const { JSDOM } = jsdom;
const { window } = new JSDOM();
const { document } = (new JSDOM('')).window;
global.document = document;
var $ = jQuery = require('jquery')(window);
.env() is deprecated since v10. Hope this helps you or anyone who has been facing these types of issues.
As mentioned above, .env() is deprecated.
Use the following:
const { window } = new JSDOM(``, { runScripts: "dangerously" });
const myLibrary = fs.readFileSync("../../whatever.js", { encoding: "utf-8" });
const scriptEl = window.document.createElement("script");
scriptEl.textContent = myLibrary;
window.document.body.appendChild(scriptEl);
In regard to the answer above, and from the jsdom docs:
Don't stuff jsdom globals onto the Node global
A common antipattern we see when people use jsdom is copying globals
from a jsdom window onto the Node.js global, and then trying to run
the code---intended for a browser---inside Node.js. This is very bad
and you should not do it. It runs code intended for the web browser in
some kind of hybrid franken-environment polluted with a ton of globals
that don't make sense there, and loses all benefits of isolating your
code into a jsdom window.
https://github.com/jsdom/jsdom/wiki/Don%27t-stuff-jsdom-globals-onto-the-Node-global
Step 1: npm install jquery
Step 2: npm install jsdom
<!-- language: lang-js -->
//add dummy function to test jquery in Node
function fn1( value ){ console.log( "fn1 says " + value );}
function fn2( value ) {console.log( "fn2 says " + value ); return false;}
var jsdom = require('jsdom');
const { JSDOM } = jsdom;
const { window } = new JSDOM();
const { document } = (new JSDOM('')).window;
//comment out the line below it create problem
//global.document = document;
var $ = jQuery = require('jquery')(window);
var callbacks = $.Callbacks();
callbacks.add(fn1);
callbacks.fire("foo!");
callbacks.add( fn2 );
callbacks.fire( "fool!" );
I am using the gulp and hercule package on node.js to transclude some plain text files. On Unix, everything seems to work fine. However, some coworkers are having issues running it on Windows. They are getting the following error message only when running on Windows:
[13:02:01] TypeError: Cannot read property 'toString' of null at Object.transcludeStringSync (D:\project\node_modules\hercule\lib\hercule.js:136:36)
I have tried the above with hercule#3.0.5 as well as hercule#2.0.5, and both packages give the above error. However, given that this occurs only on Windows and across many versions of the package, I suspect this issue has something to due with the Node.js installation or path.
The code that is using the hercule package:
var fs = require('fs');
var path = require('path');
var gulp = require('gulp');
var drakov = require('drakov');
var hercule = require('hercule');
gulp.task('mock', ['i18n','build_minify_no_tests'], function() {
var mockSpecificationTemplate= fs.readFileSync('test/mock/mock-template.apib','utf8');
var transcludedMockSpecification = hercule.transcludeStringSync(mockSpecificationTemplate, {
relativePath: path.resolve('../../../')
});
fs.writeFileSync('test/mock/mock.apib', transcludedMockSpecification, 'utf-8');
// Running mock server
var drakovArgv = {
sourceFiles: 'test/mock/mock.apib',
serverPort: 9000,
staticPaths: [
'../../'
],
discover: true,
watch: true
};
drakov.run(drakovArgv);
});
node and npm version information:
$ node -v
v6.3.0
$ npm -v
3.10.3
hercule.transcludeStringSync simply runs another hercule process and sends input to it:
const result = childProcess.spawnSync('../bin/hercule', syncArgs, syncOptions);
with the script ../bin/hercule:
#!/usr/bin/env node
"use strict";
require('../lib/main.js');
...obviously doesn't work on Windows
If that task must be synchronized, you may use the following function instead:
function transcludeStringSync(input, options) {
const {dirname, join} = require('path')
const hercule = join(dirname(require.resolve('hercule')), 'main')
const args = [hercule, '--reporter', 'json-err']
for (let name in options) {
args.push(`--${name}`, `--${options[name]}`)
}
const result = require('child_process').spawnSync('node', args, {input})
const err = result.stderr.toString()
if (err) throw new Error('Could not transclude input')
return result.stdout.toString()
}
I'm trying to write a benchmark, using benchmark.js, for some popular node.js unzip libs, mainly adm-zip, yauzl & unzip. However, I'm not sure if I've written the benchmark code correctly, because I keep getting Error: UNKNOWN, open 'file-<unzip-lib>.zip' errors for the libs that unzip asynchronously.
I created 3 copies of a sample zip file file-<unzip-lib>.zip, one for each library to work on.
Here's the code:
"use strict";
var fs = require("fs");
var Benchmark = require("benchmark");
var AdmZip = require("adm-zip"),
yauzl = require("yauzl"),
unzip = require("unzip");
var suite = new Benchmark.Suite;
var entryFile = "file.xml",
targetDir = "./unzipped/";
suite
.add("Adm-Zip#extractEntryTo", function() {
var zip = new AdmZip("./file-adm-zip.zip");
zip.extractEntryTo(entryFile, targetDir + "adm-zip/", /*maintainEntryPath*/false, /*overwrite*/true);
})
.add("YAUZL#open", function() {
yauzl.open("./file-yauzl.zip", function(err, zip) {
if (err) throw err;
zip.on("entry", function(entry) {
if (entryFile === (entry.fileName)) {
zip.openReadStream(entry, function(err, readStream) {
if (err) throw err;
// ensure parent directory exists, and then:
readStream.pipe(fs.createWriteStream(targetDir + "yauzl/" + entry.fileName));
});
}
});
zip.once("end", function() {
console.log("[YAUZL] Closing zip");
zip.close();
});
});
})
.add("UNZIP#Parse", function() {
fs.createReadStream("./file-unzip.zip")
.pipe(unzip.Parse())
.on("entry", function (entry) {
var fileName = entry.path;
if (fileName === entryFile) {
entry.pipe(fs.createWriteStream(targetDir + "unzip/" + fileName));
} else {
entry.autodrain();
}
})
.on("close", function() {
console.log("[UNZIP] Closing zip");
});
})
// add listeners
.on("cycle", function(event) {
console.log(String(event.target));
})
.on("complete", function() {
console.log("Fastest is " + this.filter("fastest").pluck("name"));
})
// run async
.run({ "async": true });
Is it failing because the streams haven't been closed properly? I'm not entirely sure this is the case, because I do see, for example, the [YAUZL] Closing zip message being displayed each time the yauzl test is run.
Here's a sample run:
$ node benchmark-unzippers.js
Adm-Zip#extractEntryTo x 2.56 ops/sec ±1.62% (11 runs sampled)
[YAUZL] Closing zip
[YAUZL] Closing zip
[YAUZL] Closing zip
[YAUZL] Closing zip
~/benchmark-unzippers.js:23
if (err) throw err;
^
Error: UNKNOWN, open 'file-yauzl.zip'
Not entirely sure what's going on here.
I ran into a similar problem in typescript and realized that the filestream to which I was writing to was not being closed before I was calling yauzl.
So I waited for the close event on the filestream before I invoked yauzl.
You might want to try the C# equivalent for close event on the filestream.