javascript-studioStudio Log 2
👻 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!
Features
- API designed to produce expressive source code.
- Uses topics instead of log levels for more fine grained filtering.
- Uses object streams to avoid serialize -> parse -> serialize when used in a command line application.
- Disabled by default. If no output stream is specified, no logs are written.
Usage
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
Install
❯ npm i @studio/log
Topics
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.
Log format
ns: The logger instance namespace.ts: The timestamp as returned byDate.now().topic: The topic name.msg: The message.data: The data.stack: The stack of error object.cause: The cause stack oferror.causeobject, if available.
API
Creating a logger
log = logger(ns[, data]): Creates a new logger with the given namespace. The namespace is added to each log entry as thensproperty. Ifdatais provided, it is added to each log entry. Multiple calls with the samensproperty 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 anddatais merged. Multiple calls with the samensproperty return the same logger instance while data is replaced.
Log instance API
log.{topic}([message][, data][, error]): Create a new log entry with these behaviors:- The
topicis added as the"topic". - If
messageis present, it's added as the"msg". - If
datais present, it's added as the"data". - If
erroris present, thestackproperty of the error is added as the"stack". If nostackis present, thetoStringrepresentation of the error is used. - If
error.codeis present, it is added to the"data"without modifying the original object. - If
error.causeis present, thestackproperty of the cause is added as the"cause". If nostackis present, thetoStringrepresentation of the cause is used. - If
error.cause.codeis present, acauseobject is added to the"data"with{ code: cause.code }and without modifying the original object.
- The
Module API
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
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`);
}
});
Related modules
- 🌈 Studio emojilog is a command line tool that parses and pretty prints the Studio Log ndjson format.
- ☯️ Studio ndjson can be used to parse the ndjson produced by Studio log.
- 🎩 Studio Log Format pretty prints Studio Log streams.
- ❎ Studio Log X x-out confidential data in log entries.
- 🏷 Studio Log Topics defines the topics used by Studio Log.
- 📦 Studio Changes is used to create the changelog for this module.
License
MIT