browser-bunyan

This package is an adaptation of, the Node logging library, Bunyan but specifically for the browser.

Although Bunyan does support being Browserified, it is still a bit bloated with features which aren't relevant in a browser environment. You can expect a Browserified and Gzipped node-bunyan to be around 27kb whereas browser-bunyan is 3.5kb, including its built-in log streams. With ES Modules and tree-shaking this can be reduced further.

Current status

Browser Bunyan was originally forked from an already mature library with a rich feature set and stable API. Furthermore, the browser environment is less complex than the server (no real streams etc). Consequently, I've found it doesn't need much work. Hopefully this is a testament to the quality of the codebase. So, don't be too concerned if you don't see that much activity in this repo. Please do raise issues for bugs, feature requests and ideas.

Install

npm install browser-bunyan --save

Usage

Import

You can access Browser Bunyan's API using:

ES modules:

import { createLogger } from 'browser-bunyan';
const logger = createLogger({ name: 'my-logger' });
logger.info('hi on info');

CommonJS

const { createLogger } = require('browser-bunyan');
const logger = createLogger({ name: 'my-logger' });
logger.debug('hi on debug');

Browser global

To use as a global, include as a standard script tag:

<script src="https://unpkg.com/browser-bunyan@1.4.0/lib/index.umd.js"></script>

now bunyan will be available as a global.

const logger = bunyan.createLogger({ name: 'my-logger' });
logger.warn('hi on warning');

Built-in Log Streams

Bunyan uses "log streams" to customize how each log record is processed. You can write your own to do whatever you want or use the built-in log streams which output log records to the console:

Console Formatted Stream

The core library also includes a dedicated browser console stream with nice formatting:

Use it like this:

import { createLogger, INFO, stdSerializers } from 'browser-bunyan';
import { ConsoleFormattedStream } from '@browser-bunyan/console-formatted-stream';

const log = createLogger({
    name: 'myLogger',
    streams: [
        {
            level: INFO, // or use the string 'info'
            stream: new ConsoleFormattedStream()
        }
    ],
    serializers: stdSerializers,
    src: true,
});

log.info('hi on info');

logByLevel

By default this stream will use console.log for all logging. Pass the option logByLevel to the ConsoleFormattedStream constructor to use the Console API's level specific logging methods (console.error, console.warn, console.info and console.debug). E.g.

new ConsoleFormattedStream( { logByLevel: true } );

Please note that if you use this option your browser's console may also filter out log output based on level, in addition to the Bunyan stream's log level.

Colors

The colors/css used by ConsoleFormattedStream are customizable:

new ConsoleFormattedStream({
    css: {
        levels : {
            trace: 'color: DeepPink',
            debug: 'color: GoldenRod',
            info: 'color: DarkTurquoise',
            warn: 'color: Purple',
            error: 'color: Crimson',
            fatal: 'color: Black',
        },
        def: 'color: DimGray',
        msg : 'color: SteelBlue',
        src : 'color: DimGray; font-style: italic; font-size: 0.9em',
    }
});

or

const css = ConsoleFormattedStream.getDefaultCss();
css.msg = 'color: cyan';
new ConsoleFormattedStream({ css });

Console Raw Stream

This logs the raw log record objects directly to the console.

import { createLogger, INFO } from 'browser-bunyan';
import { ConsoleRawStream } from '@browser-bunyan/console-raw-stream';

const log = createLogger({
    name: 'myLogger',
    stream: {
        level: INFO,
        stream: new ConsoleRawStream(),
    }
});

Console Plain Stream

This stream is similar to ConsoleFormattedStream but does not have colors. This is useful for environments where the console does not support console styling with CSS (%c).

import { createLogger, INFO } from 'browser-bunyan';
import { ConsolePlainStream } from '@browser-bunyan/console-plain-stream';

const log = createLogger({
    name: 'myLogger',
    stream: {
        level: INFO,
        stream: new ConsolePlainStream()
    }
});

logByLevel

The logByLevel option is supported in the same way as ConsoleFormattedStream.

Additional log streams

These streams are not built in to the main Browser Bunyan build. You must install them separately.

Server Stream

The Server Stream sends log records to a server endpoint. You will typically want to set the log level for server streams to warn, error or fatal - log records that are for exceptions.

Install

npm install @browser-bunyan/server-stream

To use as a global include the script tag:

<script src="https://unpkg.com/@browser-bunyan/server-stream@1.4.0/lib/index.umd.js"></script>

Usage

import { createLogger, WARN } from 'browser-bunyan';
import { ServerStream } from '@browser-bunyan/server-stream';


const log = createLogger({
    name: 'serverLogger',
    stream: {
        level: WARN,
        stream: new ServerStream({
            url: '/client-log',
            method: 'PUT',
        }),
    },
});

Notes

• The browser's current url and user agent string will automatically be appended to the log record.

• Log records are sent to the server in JSON batches (an array of record objects) at a defined throttleInterval.

• If, within a batch, a log message is duplicated, that log record will be deduped and a count field is incremented for the single log record

• The flushOnClose option will flush any unsent log records if the browser window/tab is closed. Internally this requires Fetch API to be supported.

• A writeCondition function determines if the latest batch of records should be sent. By default, log records will not be sent if the browser is offline (navigator.onLine === false) or the current user agent is determined to be a bot/crawler. You may add your own write conditions in addition to the default conditions like so:

  new ServerStream({
     url: '/client-log',
     method: 'POST',
     writeCondition: record => {
        return ServerStream.defaultWriteCondition() && record.msg !== 'GrikkleGrass';
     },
  })

Options

Option	Default	Description
url	/log	Endpoint to send log record batches to (as JSON)
method	PUT	HTTP method to send record payload with
headers	{ Content-Type': 'application/json }	Custom HTTP request headers (in addition to the default)
withCredentials	false	withCredentials property of the underlying XMLHttpRequest object
throttleInterval	3000	How often to send log record batches (ms)
writeCondition	ServerLogStream.defaultWriteCondition	A function which must return a boolean. true if the log record can be written. i.e. included in the next batch to send.
onError	-	A handler function to invoke if the send request fails
flushOnClose	false	Experimental Send unsent log records if the browser window is closed

Custom log streams

See the Node Bunyan docs below for more information on how to create you own custom stream(s).

This gist for a "server-stream" is also good example of how to write a log stream that sends log records to the server.

Browser specific features

Logging objects to the console

As per, Bunyan's log API, if you log an object under the field obj as the first argument, Browser Bunyan's built-in log streams will log this object directly to the console:

var myObject = { x: 1, y: 2 };
logger.info({ obj: myObject }, 'This is my object:');

Stream types

Node Bunyan supports various types of streams. In Browser Bunyan, streams are always of type 'raw'.

Features shared with Node Bunyan

The following docs are the node-bunyan docs at time of forking, with necessary modifications and documentation for the stripped features also removed:

Overview of features

• elegant log method API
• extensible streams system for controlling where log records go (to the console, local storage, the server, etc) src: true
• lightweight specialization of Logger instances with log.child
• custom rendering of logged objects with "serializers"

Introduction

Like most logging libraries you create a Logger instance and call methods named after the logging levels:

const { createLogger } = require('browser-bunyan');
const log = createLogger({name: 'myapp'});
log.info('hi');
log.warn({lang: 'fr'}, 'au revoir');

All loggers must provide a "name". This is somewhat akin to the log4j logger "name", but Bunyan doesn't do hierarchical logger names.

Bunyan log records are JSON. A few fields are added automatically: "time" and "v".

    {"name":"myapp","hostname":"banana.local","pid":40161,"level":30,"msg":"hi","time":"2013-01-04T18:46:23.851Z","v":0}
    {"name":"myapp","hostname":"banana.local","pid":40161,"level":40,"lang":"fr","msg":"au revoir","time":"2013-01-04T18:46:23.853Z","v":0}

Constructor API

const { createLogger } = require('browser-bunyan');
const log = createLogger({
    name: <string>,                     // Required
    level: <level constant or string>,  // Optional, see "Levels" section
    stream: <LogStream>,                // Optional, see "Streams" section
    streams: <StreamOptions[]>          // Optional, see "Streams" section
    serializers: <serializers mapping>, // Optional, see "Serializers" section
    src: <boolean>,                     // Optional, see "Core fields" section

    // Any other fields are added to all log records as is.
    foo: 'bar',
    ...
});

Log Method API

The example above shows two different ways to call log.info(...). The full API is:

log.info();     // Returns a boolean: is the "info" level enabled?
                // This is equivalent to `log.isInfoEnabled()` or
                // `log.isEnabledFor(INFO)` in log4j.

log.info('hi');                     // Log a simple string message (or number).
log.info('hi %s', bob, anotherVar); // Uses `util.format` for msg formatting.

log.info({foo: 'bar'}, 'hi');
                // Adds "foo" field to log record. You can add any number
                // of additional fields here.

log.info(err);  // Special case to log an `Error` instance to the record.
                // This adds an "err" field with exception details
                // (including the stack) and sets "msg" to the exception
                // message.
log.info(err, 'more on this: %s', more);
                // ... or you can specify the "msg".

Note that this implies you cannot pass any object as the first argument to log it. IOW, log.info(mywidget) may not be what you expect. Instead of a string representation of mywidget that other logging libraries may give you, Bunyan will try to JSON-ify your object. It is a Bunyan best practice to always give a field name to included objects, e.g.:

log.info({widget: mywidget}, ...)

This will dove-tail with Bunyan serializer support, discussed later.

The same goes for all of Bunyan's log levels: log.trace, log.debug, log.info, log.warn, log.error, and log.fatal. See the levels section below for details and suggestions.

Streams Introduction

By default, log output is to the browser console and at the "info" level. Explicitly that looks like:

import { createLogger, ConsoleRawStream } from 'browser-bunyan';
var log = createLogger({
    name: 'myapp',
    stream: new ConsoleRawStream()
    level: 'info'
});

That is an abbreviated form for a single stream. You can define multiple streams at different levels.

const log = createLogger({
  name: 'myapp',
  streams: [
    {
      level: 'info',
      stream: new ConsoleRawStream()  // log INFO and above to console
    },
    {
      level: 'error',
      path: new PostToServerStream()  // record errors on the server
    }
  ]
});

More on streams in the Streams section below.

log.child

Bunyan has a concept of a child logger to specialize a logger for a sub-component of your application, i.e. to create a new logger with additional bound fields that will be included in its log records. A child logger is created with log.child(...).

In the following example, logging on a "Wuzzle" instance's this.log will be exactly as on the parent logger with the addition of the widget_type field:

    const { createLogger } = require('browser-bunyan');
    const log = createLogger({name: 'myapp'});

    function Wuzzle(options) {
        this.log = options.log.child({widget_type: 'wuzzle'});
        this.log.info('creating a wuzzle')
    }
    Wuzzle.prototype.woos = function () {
        this.log.warn('This wuzzle is woosey.')
    }

    log.info('start');
    var wuzzle = new Wuzzle({log: log});
    wuzzle.woos();
    log.info('done');

Running that looks like (raw):

{"name":"myapp","level":30,"msg":"start","time":"2013-01-04T07:47:25.814Z"}
{"name":"myapp","widget_type":"wuzzle","level":30,"msg":"creating a wuzzle","time":"2013-01-04T07:47:25.815Z"}
{"name":"myapp","widget_type":"wuzzle","level":40,"msg":"This wuzzle is woosey.","time":"2013-01-04T07:47:25.815Z"}
{"name":"myapp","level":30,"msg":"done","time":"2013-01-04T07:47:25.816Z"}

For streams such as Console Formatted Stream and Console Plain Stream, adding the field childName will display a child stream's name suffixed to the parent logger name. For example:

    const log = createLogger({name: 'myapp'});
    const childLog = log.child({widget_type: 'wuzzle', childName: 'sub'});
    // prints "myapp/sub" as the name in console output

Serializers

Bunyan has a concept of "serializers" to produce a JSON-able object from a JavaScript object, so you can easily do the following:

log.info({req: <request object>}, 'something about handling this request');

Serializers is a mapping of log record field name, "req" in this example, to a serializer function. That looks like this:

function reqSerializer(req) {
    return {
        method: req.method,
        url: req.url,
        headers: req.headers
    }
}

const log = createLogger({
    name: 'myapp',
    serializers: {
        req: reqSerializer
    }
});

Or this:

import { createLogger, stdSerializers } from 'browser-bunyan';

const log = createLogger({
    name: 'myapp',
    serializers: {req: stdSerializers.req}
});

because Bunyan includes a small set of standard serializers. To use all the standard serializers you can use:

    import { createLogger, stdSerializers } from 'browser-bunyan';
    const log = createLogger({
      ...
      serializers: stdSerializers
    });

Note: Your own serializers should never throw, otherwise you'll get an ugly message on stderr from Bunyan (along with the traceback) and the field in your log record will be replaced with a short error message.

Levels

The log levels in bunyan are as follows. The level descriptions are best practice opinions.

• fatal (60): The service/app is going to stop or become unusable now. An operator should definitely look into this soon.
• error (50): Fatal for a particular request, but the service/app continues servicing other requests. An operator should look at this soon(ish).
• warn (40): A note on something that should probably be looked at by an operator eventually.
• info (30): Detail on regular operation.
• debug (20): Anything else, i.e. too verbose to be included in "info" level.
• trace (10): Logging from external libraries used by your app or very detailed application logging.

Suggestions: Use "debug" sparingly. Information that will be useful to debug errors post mortem should usually be included in "info" messages if it's generally relevant or else with the corresponding "error" event. Don't rely on spewing mostly irrelevant debug messages all the time and sifting through them when an error occurs.

Integers are used for the actual level values (10 for "trace", ..., 60 for "fatal") and constants are defined for the (bunyan.TRACE ... bunyan.DEBUG). The lowercase level names are aliases supported in the API.

Here is the API for changing levels in an existing logger:

log.level() -> INFO   // gets current level (lowest level of all streams)

log.level(INFO)       // set all streams to level INFO
log.level("info")     // set all streams to level INFO

log.levels() -> [DEBUG, INFO]   // get array of levels of all streams
log.levels(0) -> DEBUG          // get level of stream at index 0
log.levels("foo")               // get level of stream with name "foo"

log.levels(0, INFO)             // set level of stream 0 to INFO
log.levels(0, "info")           // can use "info" et al aliases
log.levels("foo", WARN)         // set stream named "foo" to WARN

Log Record Fields

This section will describe rules for the Bunyan log format: field names, field meanings, required fields, etc. However, a Bunyan library doesn't strictly enforce all these rules while records are being emitted. For example, Bunyan will add a time field with the correct format to your log records, but you can specify your own. It is the caller's responsibility to specify the appropriate format.

The reason for the above leniency is because IMO logging a message should never break your app. This leads to this rule of logging: a thrown exception from log.info(...) or equivalent (other than for calling with the incorrect signature) is always a bug in Bunyan.

A typical Bunyan log record looks like this:

{"name":"myapp","req":{"method":"GET","url":"/path?q=1#anchor","headers":{"x-hi":"Mom","connection":"close"}},"level":3,"msg":"start request","time":"2012-02-03T19:02:46.178Z","v":0}

Pretty-printed:

{
  "name": "myapp",
  "req": {
    "method": "GET",
    "url": "/path?q=1#anchor",
    "headers": {
      "x-hi": "Mom",
      "connection": "close"
    },
    "remoteAddress": "120.0.0.1",
    "remotePort": 51244
  },
  "level": 3,
  "msg": "send request",
  "time": "2012-02-03T19:02:57.534Z",
  "v": 0
}

Core fields:

• v: Required. Integer. Added by Bunyan. Cannot be overriden. This is the Bunyan log format version (require('bunyan').LOG_VERSION). The log version is a single integer. 0 is until I release a version "1.0.0" of node-bunyan. Thereafter, starting with 1, this will be incremented if there is any backward incompatible change to the log record format. Details will be in "CHANGES.md" (the change log).
• level: Required. Integer. Added by Bunyan. Cannot be overriden. See the "Levels" section.
• name: Required. String. Provided at Logger creation. You must specify a name for your logger when creating it. Typically this is the name of the service/app using Bunyan for logging.
• time: Required. String. Added by Bunyan. Can be overriden. The date and time of the event in ISO 8601 Extended Format format and in UTC, as from Date.toISOString().
• msg: Required. String. Every log.debug(...) et al call must provide a log message.
• src: Optional. Object giving log call source info. This is added automatically by Bunyan if the "src: true" config option is given to the Logger. Never use in production as this is really slow.

Go ahead and add more fields, and nested ones are fine (and recommended) as well. This is why we're using JSON. Some suggestions and best practices follow (feedback from actual users welcome).

Recommended/Best Practice Fields:

• err: Object. A caught JS exception. Log that thing with log.info(err) to get:

        "err": {
          "message": "boom",
          "name": "TypeError",
          "stack": "TypeError: boom\n    at Object.<anonymous> ..."
        },
        "msg": "boom",

Or use the `bunyan.stdSerializers.err` serializer in your Logger and
do this `log.error({err: err}, "oops")`. See "examples/err.js".

Streams

A "stream" is Bunyan's name for an output for log messages (the equivalent to a log4j Appender). A Bunyan Logger instance has one or more streams. In general streams are specified with the "streams" option:

const bunyan = require('browser-bunyan');
const log = createLogger({
    name: "foo",
    streams: [
        {
            stream: new ConsoleRawStream(),
            level: "debug"
        },
        ...
    ]
});

For convenience, if there is only one stream, it can specified with the "stream" and "level" options (internally converted to a Logger.streams).

const log = createLogger({
    name: "foo",
    stream: new ConsoleRawStream(),
    level: "debug"
});

If neither "streams" nor "stream" are specified, the default is a stream of type ConsoleRawStream at the "info" level.

stream type: raw

Note that in browser-bunyan streams are always raw

Inegrations

Angular 1.x integration:

Integrate with Angular's log provider:

adminApp.config(function($provide) {
    $provide.decorator('$log', function($delegate) {
        $delegate = bunyan.createLogger({
            name: 'myLogger',
            streams: [{
                level: 'info',
                stream: new bunyan.ConsoleFormattedStream(),
            }]
        });
        return $delegate;
    });
});

License

MIT. See LICENSE.