diagnostics

Diagnostics is an extremely small but powerful debug logger modeled after the Node.js core debugging technique.

• Allows debugging in multiple JavaScript environments such as Node.js, browsers and React-Native.
• Separated development and production builds to minimize impact on your application when bundled.
• Allows for customization of logger, messages, and much more.

Installation

The module is released in the public npm registry and can be installed by running:

npm install --save diagnostics

Usage

• Introduction
  • .enabled
  • .namespace
  • .dev/prod
• Adapters
  • process.env
  • hash
  • localStorage
  • AsyncStorage
• Modifiers
  • namespace
• Logger

Introduction

To create a new logger simply require the diagnostics module and call the returned function the namespace under which the logs should be enabled. Generally you use the name of the module or application that your developing as first (root) namespace.

const debug = require('diagnostics')('foo:bar:baz');
const debug = require('diagnostics')('foo:bar:baz', { options });

debug('this is a log message %s', 'that will only show up when enabled');
debug('that is pretty neat', { log: 'more', data: 1337 });

Please note that the returned logger is fully configured out of the box, you do not need to use any of the adapters/modifiers your self, they are there for when you want more advanced control over the process.

The returned logger exposes some addition properties that can be used used in your application or library.

enabled

The returned logger will have a .enabled property assigned to it. This boolean can be used to check if the logger was enabled:

const debug = require('diagnostics')('foo:bar');

if (debug.enabled) {
  //
  // Do something special
  //
}

namespace

This is the namespace that you originally provided to the function.

const debug = require('diagnostics')('foo:bar');

console.log(debug.namespace); // foo:bar

dev/prod

There are different builds available of diagnostics, when you create a production build of your application using NODE_ENV=production you will be given an optimized, smaller build of diagnostics to reduce your bundle size. The dev and prod booleans on the returned logger indicate if you have a production or development version of the logger.

const debug = require('diagnostics')('foo:bar');

if (debug.prod) {
  // do stuff
}

Modifiers

Modifiers allows you to programmatically alter the messages that are being logged. Modifiers are applied to all diagnostic instances. To add a new modifier you call the modify method of one the returned loggers. It receives the following arguments:

1. message, Array, the log message.
2. options, Object, the options that were passed into the logger when it was initially created.

const debug = require('diagnostics')('example:modifiers');

debug.modify(function (message, options) {
  return messages;
});

The modifiers are only enabled for development.

namespace

This modifier is enabled for all debug instances and prefixes the messages with the name of namespace under which it is logged. The namespace is colored using the colorspace module which groups similar namespaces under the same colorspace. You can have multiple namespaces for the debuggers where each namespace should be separated by a :

foo
foo:bar
foo:bar:baz

For console based output the namespace-ansi is used.

Loggers

By default it will log all messages to console.log in when the logger is enabled using the debug flag that is set using one of the adapters.

You can override the default logger by assigning your own using the set method. This method accepts a function as first argument which will be called every time a message needs to be logged.

const debug = require('diagnostics')('foo:more:namespaces');

debug.use(function logger(meta, args) {
  console.log(meta);
  console.debug(...args);
});

The assigned logger will receive 2 arguments:

1. meta An object with all the options that was provided to the original logger that wants to write the log message as well as properties of the debugger such as prod, dev, namespace, enabled.
2. args An array of the log messages that needs to be written.

Adapters

Adapters allows diagnostics to pull the DEBUG and DIAGNOSTICS environment variables from different sources. Not every JavaScript environment has a process.env that we can leverage. Adapters allows us to have different adapters for different environments. It means you can write your own custom adapter if needed as well.

The adapter function should be passed a function as argument, this function will receive the namespace of a logger as argument and it should return a boolean that indicates if that logger should be enabled or not.

const debug = require('diagnostics')('example:namespace');

debug.adapter(require('diagnostics/adapters/localstorage'));

The modifiers are only enabled for development. The following adapters are available are available:

process.env

This adapter is enabled for node.js.

Uses the DEBUG or DIAGNOSTICS (both are recognized) environment variables to pass in debug flag:

UNIX/Linux/Mac

DEBUG=foo* node index.js

Using environment variables on Windows is a bit different, and also depends on toolchain you are using:

Windows

set DEBUG=foo* & node index.js

Powershell

$env:DEBUG='foo*';node index.js

hash

This adapter is enabled for browsers.

This adapter uses the window.location.hash of as source for the environment variables. It assumes that hash is formatted using the same syntax as query strings:

http://example.com/foo/bar#debug=foo*

It triggers on both the debug= and diagnostics= names.

localStorage

This adapter is enabled for browsers.

License

MIT