polog

polog is one of the fastest and simplest Node.js logging library that behaves as the standard console command. It adds some sugar as timestamp and log levels. This library uses as little processing power as possible to avoid affecting Node.js event loop.

Logging (in Node.js) should always use stdout/stderr and leave advanced logging manipulation to the rest of the stack. For best performance and asynchronous operation you should use pipes on Linux as mentioned in official docs. This also enables you to do file logging as efficiently as possible.

console uses process.stdout.write which has the same behaviour as this library.

Installation

npm install polog

Options

Options can be passed as object before creation.

debug - enable output of .debug function, if set to false (default) it won't print anything

const log = require('polog')({ debug: true })
log.debug("will be shown")

format - enable usage of util.format, ie:

const log = require('polog')({ format: true })
polog.log("test: %d", Math.random())

if disabled (default), which is faster, use ES6 template strings

polog.log("test: ${Math.random()}")

prefix - prefix messages with custom output, default is Date.now

const log = require("../index.js")({ prefix: () => { return (new Date).toISOString() }})

Keep in mind that this is also called on every message output, so you want to keep it as simple as possible.

Levels

There are four standard levels:

info I - standard stdout output

debug D - debug stdout output, depens on debug options, useful for (NON)PRODUCTION environment switching

warn W - stderr warnings output

error E - stderr error output

Currently there is no way to add new levels, if that is wanted, please open an issue.

Standard logging

const log = require('polog')({ debug: true })

log.debug("debug mode") // shown only when debug is set to true above
log.info("hello there!")
log.warn("be careful")
log.error("not good")

This will output:

1494005876469 D debug mode
1494005876469 I hello there!
1494005876470 W be careful
1494005876470 E not good

Using format option:

const log = require('polog')({ format: true })

log.info("test message: %d", Math.random())

outputs:

// # 1494006079148 I test message: 0.17100814691155053

This calls util.format that is also used by console.* functions. It is slower since every message has to be processed first. It is recommended to use ES6 template string instead:

const log = require('polog')()

log.info(`test message: ${Math.random()}`)

Changing prefix:

const log = require("../index.js")({ prefix: () => { return (new Date).toISOString()}})

log.info("test message")

outputs:

2017-05-05T17:53:05.702Z I test message

This is probably more user friendly, altough default Date.now is faster since Date object doesn't have to be created for every function call.

Fast file logging on Linux

Redirect (pipe) all logs to a file asynchronously

node app.js > app.log 2>&1

Split standard and error logs

node app.js > access.log 2>error.log