The logger that npm uses

License: ISC

Language: JavaScript


The logger util that npm uses.

This logger is very basic. It does the logging for npm. It supports custom levels and colored output.

By default, logs are written to stderr. If you want to send log messages to outputs other than streams, then you can change the member, or you can just listen to the events that it emits, and do whatever you want with them.


npm install npmlog --save

Basic Usage

var log = require('npmlog')

// additional stuff ---------------------------+
// message ----------+                         |
// prefix ----+      |                         |
// level -+   |      |                         |
//        v   v      v                         v'fyi', 'I have a kitty cat: %j', myKittyCat)


  • {String}

The level to display logs at. Any logs at or above this level will be displayed. The special level silent will prevent anything from being displayed ever.


  • {Array}

An array of all the log messages that have been entered.


  • {Number}

The maximum number of records to keep. If log.record gets bigger than 10% over this value, then it is sliced down to 90% of this value.

The reason for the 10% window is so that it doesn't have to resize a large array on every log entry.


  • {Object}

A style object that specifies how prefixes are styled. (See below)


  • {Object}

A style object that specifies how the heading is styled. (See below)


  • {String} Default: ""

If set, a heading that is printed at the start of every line.

  • {Stream} Default: process.stderr

The stream where output is written.


Force colors to be used on all messages, regardless of the output stream.


Disable colors on all messages.


Enable the display of log activity spinner and progress bar


Disable the display of a progress bar


Force the unicode theme to be used for the progress bar.


Disable the use of unicode in the progress bar.


Set a template for outputting the progress bar. See the gauge documentation for details.


Select a themeset to pick themes from for the progress bar. See the gauge documentation for details.


Stop emitting messages to the stream, but do not drop them.


Emit all buffered messages that were written while paused.

log.log(level, prefix, message, ...)

  • level {String} The level to emit the message at
  • prefix {String} A string prefix. Set to "" to skip.
  • message... Arguments to util.format

Emit a log message at the specified level.

log[level](prefix, message, ...)

For example,

  • log.silly(prefix, message, ...)
  • log.verbose(prefix, message, ...)
  •, message, ...)
  • log.http(prefix, message, ...)
  • log.warn(prefix, message, ...)
  • log.error(prefix, message, ...)

Like log.log(level, prefix, message, ...). In this way, each level is given a shorthand, so you can do, message).

log.addLevel(level, n, style, disp)

  • level {String} Level indicator
  • n {Number} The numeric level
  • style {Object} Object with fg, bg, inverse, etc.
  • disp {String} Optional replacement for level in the output.

Sets up a new level with a shorthand function and so forth.

Note that if the number is Infinity, then setting the level to that will cause all log messages to be suppressed. If the number is -Infinity, then the only way to show it is to enable all log messages.

log.newItem(name, todo, weight)

  • name {String} Optional; progress item name.
  • todo {Number} Optional; total amount of work to be done. Default 0.
  • weight {Number} Optional; the weight of this item relative to others. Default 1.

This adds a new are-we-there-yet item tracker to the progress tracker. The object returned has the log[level] methods but is otherwise an are-we-there-yet Tracker object.

log.newStream(name, todo, weight)

This adds a new are-we-there-yet stream tracker to the progress tracker. The object returned has the log[level] methods but is otherwise an are-we-there-yet TrackerStream object.

log.newGroup(name, weight)

This adds a new are-we-there-yet tracker group to the progress tracker. The object returned has the log[level] methods but is otherwise an are-we-there-yet TrackerGroup object.


Events are all emitted with the message object.

  • log Emitted for all messages
  • log.<level> Emitted for all messages with the <level> level.
  • <prefix> Messages with prefixes also emit their prefix as an event.

Style Objects

Style objects can have the following fields:

  • fg {String} Color for the foreground text
  • bg {String} Color for the background
  • bold, inverse, underline {Boolean} Set the associated property
  • bell {Boolean} Make a noise (This is pretty annoying, probably.)

Message Objects

Every log event is emitted with a message object, and the log.record list contains all of them that have been created. They have the following fields:

  • id {Number}
  • level {String}
  • prefix {String}
  • message {String} Result of util.format()
  • messageRaw {Array} Arguments to util.format()

Blocking TTYs

We use set-blocking to set stderr and stdout blocking if they are tty's and have the setBlocking call. This is a work around for an issue in early versions of Node.js 6.x, which made stderr and stdout non-blocking on OSX. (They are always blocking Windows and were never blocking on Linux.) npmlog needs them to be blocking so that it can allow output to stdout and stderr to be interlaced.

Project Statistics

Sourcerank 17
Repository Size 129 KB
Stars 309
Forks 48
Watchers 34
Open issues 21
Dependencies 267
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Tags 28
Last updated
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Top Contributors See all

Rebecca Turner isaacs Forrest L Norvell Kat Marchán Audrey Eschright Max Ogden James Talmage Bryan English Zearin Richard Smith-Unna helio-frota Rick Waldron

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Recent Tags See all

v4.1.2 June 26, 2017
v4.1.1 June 26, 2017
v4.1.0 May 05, 2017
v4.0.2 December 12, 2016
v4.0.1 November 17, 2016
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v3.1.2 June 16, 2016
v3.1.1 June 16, 2016
v3.1.0 June 16, 2016
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v2.0.4 May 19, 2016
v2.0.3 March 16, 2016
v2.0.2 January 28, 2016
v2.0.1 January 21, 2016
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