jobi

Tiny logging utility with events, streams, and sane defaults.

const logger = require('@starryinternet/jobi');
logger.warn(`Soon we'll be jobiing our logs 🤯`);

Lore

Jobi is a fictional tree from Thomas the Tank Engine that is logged. That's all folks.

Features

• Pretty (default), JSON, and custom formats
• Configurable stdout and stderr streams
• Singleton by default
• Shared or local format and level
• Error stack serialization

Levels

stdout

• trace
• debug
• info

stderr

• warn
• error
• critical

Each value implicitly includes all levels above itself – so, for example, when your app is run with NODE_DEBUG=warn node app.js, all warn, error, and critical logs will be sent to stdout/stderr. In the same example, logger.info() and logger.debug() would effectively be no-ops.

API

logger.log(level, message, [...interpolationValues])

• level (string): one of the levels defined above
• message (string): an optional message. If the message is a format string, it will use the interpolationValues as the format parameters.
• [...interpolationValues] (...any): optional values to use to format the message using util.format(). Otherwise, these values will be appended to the message.

logger.<level>(message, [interpolationValues])

The same as logger.log, but without the need to pass the level as a parameter. Prefer using these to logger.log.

logger.format (Log => string)

Get the current log format OR set the current log format for this Jobi instance. By default, a Jobi instance will use the shared log format. Set logger.format = null to resume using the shared log format.

Log:

• timestamp (string)
• level (string)
• message (string | undefined) prefix is prepended to message

logger.prefix (string)

Get the current log prefix of a Jobi instance. Prefixes can only be set in the constructor.

Jobi.level (string)

Get the shared log level OR set the shared log level.

Jobi.format (Log => string)

Get the shared log format OR set the shared log format.

new Jobi(opts)

opts

• [format] (string | (Log => string))
• [prefix] (string)
• [stdout] (stream.Writable)
• [stderr] (stream.Writable)

Example

logger.log('info', 'This is an info log');

// Preferred
logger.info('This is another info log');

NOTE: logger.log has the same argument signature as console.log.

Configuration

Log Level

jobi will read the initial log level from the NODE_DEBUG environment variable.

The NODE_DEBUG environment variable can actually contain multiple flags, but the one with the lowest priority level will win. For example, NODE_DEBUG=debug,info,critical node app.js will use debug as the log level, since it automatically includes the other levels.

NOTE: If the log level is not set, jobi will not write any logs.

Log Format

jobi will read the initial log format from the JOBI_FORMAT environment variable.

Possible formats:

• pretty
• json

Log Prefix

A log prefix that will be prepended to the message property of a log object and can be set by passing the prefix prop to the Jobi constructor. Prefixes are added to all logs of Jobi instance. For different prefixes create separate instances.

Events

Each log level will emit an event of the same name if the log level is high enough. For example, logger.critical('foo'); will emit a 'critical' event whose callback argument will be of type Log. This way, applications can hook in to the logging system and respond however they want (post to Slack, send to a logging service, etc.).

In addition, emit a log event when any log is received if there is a listener to the event. This event will be passed with args level, formattedLog, and rawLog. Code can hook into these events to forward logs or ensure that logs are being added even if it is not being written to stdout/stderr.

Streaming

By default, logs are written to either process.stdout or process.stderr.

Apps can optionally overwrite logger.stdout and logger.stderr with other instances of stream.Writable in order to stream logs to the filesystem, via HTTP, to a database, etc.

Node.js Compatibility

jobi requires >= Node.js 8.3.

Examples

Logging

const logger = require('@starryinternet/jobi');

logger.critical( 'this is a %s with some %s', 'log', 'formatting' );

Event binding

const logger = require('@starryinternet/jobi');

logger.on( 'critical', msg => slack.notify( msg ) );
logger.on( 'error', (msg, log) => {
  slack.notify(msg);
  console.error(log.stack);
});

Streaming

const logger = require('@starryinternet/jobi');
const fs     = require('fs');

const file = fs.createWriteStream('./log.txt');
logger.stdout = file;
logger.stderr = file;

logger.info('blah blah blah');

Custom Log Format

const { Jobi } = require('@starryinternet/jobi');
const format = log => '>> ' + log.message || 'No message';

const logger = new Jobi({ format });
logger.info('Hello world'); // ">> Hello world"
logger.info(); // ">> No message"

Custom Log Prefix

const { Jobi } = require('@starryinternet/jobi');
const prefix = 'logger: ';

const logger = new Jobi({ prefix });
logger.info('Hello world'); // "[2021-11-29T15:35:59.859Z] INFO: logger: log message"