👻 A tiny JSON logger with emoji support
👻 Log ndjson to an output stream, pretty print the output with emoji ✨
Note! Version 2 has significantly changed compared to the original announcement. Make sure to read the release notes for migration instructions!
Log output is disabled by default to ensure logs don't get in the way when writing unit tests. Therefore you want to set this up as the first thing in your main:
// Sending raw ndJSON logs to stdout, e.g. in a server application:
const Stringify = require('@studio/ndjson/stringify');
require('@studio/log')
.pipe(new Stringify())
.pipe(process.stdout);
// Sending fancy formatted logs to stdout, e.g. in a command line tool:
const Format = require('@studio/log-format/fancy');
require('@studio/log')
.pipe(new Format())
.pipe(process.stdout);
// Sending logs to console.log, e.g. in a browser:
const Format = require('@studio/log-format/console');
require('@studio/log')
.pipe(new Format())
Next, create a logger instance in a module and start writing logs:
const logger = require('@studio/log');
const log = logger('app');
exports.startService = function (port) {
log.launch('my service', { port: 433 });
};
In the server example above, this output is produced:
{"ts":1486630378584,"ns":"app","topic":"launch","msg":"my service","data":{"port":433}}
Send your logs to the emojilog CLI for pretty printing:
❯ cat logs.ndjson | emojilog
09:52:58 🚀 app my service port=433
❯ npm i @studio/log
Instead of log levels, this logger uses a set of topics. Unlike log levels, topics are not ordered by severity.
These topics are available: ok
, warn
, error
, issue
, ignore
, input
,
output
, send
, receive
, fetch
, finish
, launch
, terminate
, spawn
,
broadcast
, disk
, timing
, money
, numbers
and wtf
.
Topics and their mapping to emojis are defined in the Studio Log Topics project.
ns
: The logger instance namespace.ts
: The timestamp as returned by Date.now()
.topic
: The topic name.msg
: The message.data
: The data.stack
: The stack of error object.cause
: The cause stack of error.cause
object, if available.log = logger(ns[, data])
: Creates a new logger with the given namespace.
The namespace is added to each log entry as the ns
property. If data
is
provided, it is added to each log entry. Multiple calls with the same ns
property return the same logger instance while data is replaced.log.child(ns[, data])
: Creates a child logger of a log instance. The
namespaces are joined with a blank and data
is merged. Multiple calls with
the same ns
property return the same logger instance while data is
replaced.log.{topic}([message][, data][, error])
: Create a new log entry with these
behaviors:
topic
is added as the "topic"
.message
is present, it's added as the "msg"
.data
is present, it's added as the "data"
.error
is present, the stack
property of the error is added as the
"stack"
. If no stack
is present, the toString
representation of the
error is used.error.code
is present, it is added to the "data"
without modifying
the original object.error.cause
is present, the stack
property of the cause is added
as the "cause"
. If no stack
is present, the toString
representation
of the cause is used.error.cause.code
is present, a cause
object is added to the
"data"
with { code: cause.code }
and without modifying the original
object.logger.pipe(stream)
: Configure the output stream to write logs to. If not
specified, no logs are written. Returns the stream.logger.hasStream()
: Whether a stream was set.logger.reset()
: Resets the internal state.Transform streams can be used to alter the data before passing it on. For
example, Studio Log X is a Transform stream that can remove confidential
data from the log data and Studio Log Format project implements the
basic
, fancy
and console
pretty printers.
Format transforms are node transform streams in writableObjectMode
. Here
is an example implementation, similar to the ndjson stringify transform:
const { Transform } = require('stream');
const ndjson = new Transform({
writableObjectMode: true,
transform(entry, enc, callback) {
const str = JSON.stringify(entry);
callback(null, `${str}\n`);
}
});
MIT