Axe

Axe is a logger-agnostic wrapper that normalizes logs regardless of argument style. Great for large development teams, old and new projects, and works with Pino, Bunyan, Winston, console, and more. It is lightweight, performant, highly-configurable, and automatically adds OS, CPU, and Git information to your logs. It supports hooks (useful for masking sensitive data) and dot-notation remapping, omitting, and picking of log metadata properties. Made for Forward Email, Lad, and Cabin.

Table of Contents

• Foreword
• Application Metadata and Information
• Install
  • Node
  • Browser
• Usage
  • Options
  • Supported Platforms
  • Node
  • Browser
  • Custom logger
  • Silent Logging
  • Stack Traces and Error Handling
  • Hooks
  • Remapping
  • Omitting
  • Picking
  • Aliases
  • Methods
• Examples
  • Send Logs to HTTP Endpoint
  • Send Logs to Slack
  • Suppress Logger Data
• Contributors
• License

Foreword

Axe was built to provide consistency among development teams when it comes to logging. You not only have to worry about your development team using the same approach to writing logs and debugging applications, but you also have to consider that open-source maintainers implement logging differently in their packages.

There is no industry standard as to logging style, and developers mix and match arguments without consistency. For example, one developer may use the approach of console.log('someVariable', someVariable) and another developer will simply write console.log(someVariable). Even if both developers wrote in the style of console.log('someVariable', someVariable), there still could be an underlying third-party package that logs differently, or uses an entirely different approach. Furthermore, by default there is no consistency of logs with stdout or using any third-party hosted logging dashboard solution. It will also be almost impossible to spot logging outliers as it would be too time intensive.

No matter how your team or underlying packages style arguments when invoked with logger methods, Axe will clean it up and normalize it for you. This is especially helpful as you can see outliers much more easily in your logging dashboards, and pinpoint where in your application you need to do a better job of logging at. Axe makes your logs consistent and organized.

Axe is highly configurable and has built-in functionality to remap, omit, and pick metadata fields with dot-notation support. Instead of using slow functions like lodash's omit, we use a more performant approach.

Axe adheres to the Log4j log levels, which have been established for 21+ years (since 2001). This means that you can use any custom logger (or the default console), but we strictly support the following log levels:

• trace
• debug
• info
• warn
• error
• fatal

Axe normalizes invocation of logger methods to be called with only two arguments: a String or Error as the first argument and an Object as the second argument. These two arguments are referred to as "message" and "meta" respectively. For example, if you're simply logging a message and some other information:

logger.info('Hello world', { beep: 'boop', foo: true });
// Hello world { beep: 'boop', foo: true }

Or if you're logging a user, or a variable in general:

logger.info('user', { user: { id: '1' } });
// user { user: { id: '1' } }

logger.info('someVariable', { someVariable: true });
// someVariable { someVariable: true }

You might write logs with three arguments (level, message, meta) using the log method of Axe's returned logger instance:

logger.log('info', 'Hello world', { beep: 'boop', foo: true });
// Hello world { beep: 'boop', foo: true }

Logging errors is just the same as you might do now:

logger.error(new Error('Oops!'));

// Error: Oops!
//     at REPL3:1:14
//     at Script.runInThisContext (node:vm:129:12)
//     at REPLServer.defaultEval (node:repl:566:29)
//     at bound (node:domain:421:15)
//     at REPLServer.runBound [as eval] (node:domain:432:12)
//     at REPLServer.onLine (node:repl:893:10)
//     at REPLServer.emit (node:events:539:35)
//     at REPLServer.emit (node:domain:475:12)
//     at REPLServer.Interface._onLine (node:readline:487:10)
//     at REPLServer.Interface._line (node:readline:864:8)

You might log errors like this:

logger.error(new Error('Oops!'), new Error('Another Error!'));

// Error: Oops!
//     at Object.<anonymous> (/Users/user/Projects/axe/test.js:5:14)
//     at Module._compile (node:internal/modules/cjs/loader:1105:14)
//     at Object.Module._extensions..js (node:internal/modules/cjs/loader:1159:10)
//     at Module.load (node:internal/modules/cjs/loader:981:32)
//     at Function.Module._load (node:internal/modules/cjs/loader:822:12)
//     at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:77:12)
//     at node:internal/main/run_main_module:17:47
//
// Error: Another Error!
//     at Object.<anonymous> (/Users/user/Projects/axe/test.js:5:34)
//     at Module._compile (node:internal/modules/cjs/loader:1105:14)
//     at Object.Module._extensions..js (node:internal/modules/cjs/loader:1159:10)
//     at Module.load (node:internal/modules/cjs/loader:981:32)
//     at Function.Module._load (node:internal/modules/cjs/loader:822:12)
//     at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:77:12)
//     at node:internal/main/run_main_module:17:47

Or even multiple errors:

logger.error(new Error('Oops!'), new Error('Another Error!'), new Error('Woah!'));

// Error: Oops!
//     at Object.<anonymous> (/Users/user/Projects/axe/test.js:6:3)
//     at Module._compile (node:internal/modules/cjs/loader:1105:14)
//     at Object.Module._extensions..js (node:internal/modules/cjs/loader:1159:10)
//     at Module.load (node:internal/modules/cjs/loader:981:32)
//     at Function.Module._load (node:internal/modules/cjs/loader:822:12)
//     at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:77:12)
//     at node:internal/main/run_main_module:17:47
//
// Error: Another Error!
//     at Object.<anonymous> (/Users/user/Projects/axe/test.js:7:3)
//     at Module._compile (node:internal/modules/cjs/loader:1105:14)
//     at Object.Module._extensions..js (node:internal/modules/cjs/loader:1159:10)
//     at Module.load (node:internal/modules/cjs/loader:981:32)
//     at Function.Module._load (node:internal/modules/cjs/loader:822:12)
//     at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:77:12)
//     at node:internal/main/run_main_module:17:47
//
// Error: Woah!
//     at Object.<anonymous> (/Users/user/Projects/axe/test.js:8:3)
//     at Module._compile (node:internal/modules/cjs/loader:1105:14)
//     at Object.Module._extensions..js (node:internal/modules/cjs/loader:1159:10)
//     at Module.load (node:internal/modules/cjs/loader:981:32)
//     at Function.Module._load (node:internal/modules/cjs/loader:822:12)
//     at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:77:12)
//     at node:internal/main/run_main_module:17:47

As you can see, Axe combines multiple errors into one – for an easy to read stack trace.

If you simply use logger.log, then the log level used will be info, but it will still use the logger's native log method (as opposed to using info). If you invoke logger.log (or any other logging method, e.g. logger.info, logger.warn, or logger.error), then it will consistently invoke the internal logger with these two arguments.

logger.log('hello world');
// hello world

logger.info('hello world');
// hello world

logger.warn('uh oh!', { amount_spent: 50 });
// uh oh! { amount_spent: 50 }

As you can see - this is exactly what you'd want your logger output to look like. Axe doesn't change anything out of the ordinary. Now here is where Axe is handy - it will automatically normalize argument style for you:

logger.warn({ hello: 'world' }, 'uh oh');
// uh oh { hello: 'world' }

logger.warn('uh oh', 'foo bar', 'beep boop');
// uh oh foo bar beep boop

logger.warn('hello', new Error('uh oh!'));

// Error: uh oh!
//     at Object.<anonymous> (/Users/user/Projects/axe/test.js:5:22)
//     at Module._compile (node:internal/modules/cjs/loader:1105:14)
//     at Object.Module._extensions..js (node:internal/modules/cjs/loader:1159:10)
//     at Module.load (node:internal/modules/cjs/loader:981:32)
//     at Function.Module._load (node:internal/modules/cjs/loader:822:12)
//     at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:77:12)
//     at node:internal/main/run_main_module:17:47

logger.warn(new Error('uh oh!'), 'hello');

// Error: uh oh!
//     at Object.<anonymous> (/Users/user/Projects/axe/test.js:9:13)
//     at Module._compile (node:internal/modules/cjs/loader:1105:14)
//     at Object.Module._extensions..js (node:internal/modules/cjs/loader:1159:10)
//     at Module.load (node:internal/modules/cjs/loader:981:32)
//     at Function.Module._load (node:internal/modules/cjs/loader:822:12)
//     at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:77:12)
//     at node:internal/main/run_main_module:17:47

Axe has support for format specifiers, and you can even use format specifiers in the browser (uses format-util – has limited number of format specifiers) and Node (uses the built-in util.format method – supports all format specifiers). This feature is built-in thanks to smart detection using format-specifiers.

logger.info('favorite color is %s', 'blue');
// favorite color is blue

As you can see, Axe makes your logs consistent in both Node and browser environments.

Axe's goal is to allow you to log in any style, but make your log output more readable, organized, and clean.

The most impactful feature of Axe is that it makes logger output human-friendly and readable when there are multiple errors.

Normally console output (and most other loggers) by default will output the following unreadable stack trace:

> console.log(new Error('hello'), new Error('world'));
Error: hello
    at REPL6:1:13
    at Script.runInThisContext (node:vm:129:12)
    at REPLServer.defaultEval (node:repl:566:29)
    at bound (node:domain:421:15)
    at REPLServer.runBound [as eval] (node:domain:432:12)
    at REPLServer.onLine (node:repl:893:10)
    at REPLServer.emit (node:events:539:35)
    at REPLServer.emit (node:domain:475:12)
    at REPLServer.Interface._onLine (node:readline:487:10)
    at REPLServer.Interface._line (node:readline:864:8) Error: world
    at REPL6:1:33
    at Script.runInThisContext (node:vm:129:12)
    at REPLServer.defaultEval (node:repl:566:29)
    at bound (node:domain:421:15)
    at REPLServer.runBound [as eval] (node:domain:432:12)
    at REPLServer.onLine (node:repl:893:10)
    at REPLServer.emit (node:events:539:35)
    at REPLServer.emit (node:domain:475:12)
    at REPLServer.Interface._onLine (node:readline:487:10)
    at REPLServer.Interface._line (node:readline:864:8)

However with Axe, errors and stack traces are much more readable (we use maybe-combine-errors under the hood):

> logger.log(new Error('hello'), new Error('world'));
Error: hello
    at REPL7:1:12
    at Script.runInThisContext (node:vm:129:12)
    at REPLServer.defaultEval (node:repl:566:29)
    at bound (node:domain:421:15)
    at REPLServer.runBound [as eval] (node:domain:432:12)
    at REPLServer.onLine (node:repl:893:10)
    at REPLServer.emit (node:events:539:35)
    at REPLServer.emit (node:domain:475:12)
    at REPLServer.Interface._onLine (node:readline:487:10)
    at REPLServer.Interface._line (node:readline:864:8)

Error: world
    at REPL7:1:32
    at Script.runInThisContext (node:vm:129:12)
    at REPLServer.defaultEval (node:repl:566:29)
    at bound (node:domain:421:15)
    at REPLServer.runBound [as eval] (node:domain:432:12)
    at REPLServer.onLine (node:repl:893:10)
    at REPLServer.emit (node:events:539:35)
    at REPLServer.emit (node:domain:475:12)
    at REPLServer.Interface._onLine (node:readline:487:10)
    at REPLServer.Interface._line (node:readline:864:8)

Lastly, Axe works in both server-side and client-side environments (with Node and the browser).

Application Metadata and Information

If you've read the Foreword, you'll know that Axe invokes logger methods with two normalized arguments, message (String or Error) and meta (Object).

Axe will automatically add the following metadata and information to the meta Object argument passed to logger methods:

⚠️ Note that by default, Axe will not output this additional information for you (since we set the meta.omittedFields option to [ 'level', 'err', 'app', 'args' ] by default).

Axe will omit from metadata all properties via the default Array from meta.omittedFields option (see Options below for more insight).

If the argument "meta" is an empty object, then it will not be passed as an argument to logger methods *ndash; because you don't want to see an empty {} polluting your log metadata. Axe keeps your log output tidy.

If you set meta.omittedFields to an empty Array, or alternatively use the environment variable AXE_OMIT_META_FIELDS="", then application information will be visible:

const Axe = require('axe');

const logger = new Axe({
  meta: {
    omittedFields: []
    // NOTE: the default is `[ 'level', 'err', 'app', 'args' ]`
  }
});

// hello world {
//   args: [ 'info', 'hello world' ],
//   level: 'info',
//   app: {
//     name: 'axe',
//     version: '10.0.0',
//     node: 'v16.15.1',
//     hash: '5ecd389b2523a8e810416f6c4e3ffa0ba6573dc2',
//     tag: 'v10.0.0',
//     environment: 'development',
//     hostname: 'users-MacBook-Air.local',
//     pid: 3477,
//     cluster: { isMaster: true, isWorker: false, schedulingPolicy: 2 },
//     os: {
//       arch: 'arm64',
//       cpus: [Array],
//       endianness: 'LE',
//       freemem: 271433728,
//       priority: 0,
//       homedir: '/Users/user',
//       hostname: 'users-MacBook-Air.local',
//       loadavg: [Array],
//       network_interfaces: [Object],
//       platform: 'darwin',
//       release: '21.3.0',
//       tmpdir: '/var/folders/rl/gz_3j8fx4s98k2kb0hknfygm0000gn/T',
//       totalmem: 17179869184,
//       type: 'Darwin',
//       uptime: 708340,
//       user: [Object],
//       version: 'Darwin Kernel Version 21.3.0: Wed Dec  8 00:40:46 PST 2021; root:xnu-8019.80.11.111.1~1/RELEASE_ARM64_T8101'
//     },
//     worker_threads: {
//       isMainThread: true,
//       resourceLimits: {},
//       threadId: 0,
//       workerData: null
//     }
//   }
// }

We recommend that you set meta.omittedFields to an empty Array in production environments for verbosity.

Note that you can also combine meta.omittedFields with meta.pickedFields and meta.remappedFields (in case you want to output specific properties from meta.app and exclude others – see Options for more insight).

Install

Node

npm:

npm install axe

Browser

See Browser usage below for more information.

Usage

Options

Supported Platforms

• Node: v14+

• Browsers (see .browserslistrc):

  npx browserslist

  and_chr 102
  and_ff 101
  and_qq 10.4
  and_uc 12.12
  android 101
  chrome 103
  chrome 102
  chrome 101
  chrome 100
  edge 103
  edge 102
  edge 101
  firefox 101
  firefox 100
  firefox 91
  ios_saf 15.5
  ios_saf 15.4
  ios_saf 15.2-15.3
  ios_saf 15.0-15.1
  ios_saf 14.5-14.8
  ios_saf 14.0-14.4
  ios_saf 12.2-12.5
  kaios 2.5
  op_mini all
  op_mob 64
  opera 86
  opera 85
  safari 15.5
  safari 15.4
  samsung 17.0
  samsung 16.0

Node

const Axe = require('axe');

const logger = new Axe();

logger.info('hello world');

Browser

This package requires Promise support, therefore you will need to polyfill if you are using an unsupported browser (namely Opera mini).

We no longer support IE as of Axe v10.0.0+.

VanillaJS

The browser-ready bundle is only 18 KB when minified and 6 KB when gzipped.

<script src="https://polyfill.io/v3/polyfill.min.js?features=Promise"></script>
<script src="https://unpkg.com/axe"></script>
<script type="text/javascript">
  (function () {
    // make a new logger instance
    const logger = new Axe();
    logger.info('hello world');

    // or you can override console everywhere
    console = new Axe();
    console.info('hello world');
  });
</script>

Required Browser Features

We recommend using https://polyfill.io (specifically with the bundle mentioned in VanillaJS above):

<script src="https://polyfill.io/v3/polyfill.min.js?features=Promise"></script>

• Promise is not supported in op_mini all

Bundler

If you're using something like browserify, webpack, or rollup, then install the package as you would with Node above.

Custom logger

By default, Axe uses the built-in console (with console-polyfill for cross-browser support).

However you might want to use something fancier, and as such we support any logger out of the box.

Loggers supported include, but are not limited to:

• consola
• pino
• signale
• bunyan
• winston
• high-console

Just pass your custom logging utility as the logger option:

const signale = require('signale');
const Axe = require('axe');

const logger = new Axe({ logger: signale });

logger.info('hello world');

In Lad, we have an approach similar to the following, where non-production environments use consola, and production environments use pino.

const Axe = require('axe');
const consola = require('consola');
const pino = require('pino')({
  customLevels: {
    log: 30
  },
  hooks: {
    // <https://github.com/pinojs/pino/blob/master/docs/api.md#logmethod>
    logMethod(inputArgs, method) {
      return method.call(this, {
        // <https://github.com/pinojs/pino/issues/854>
        // message: inputArgs[0],
        msg: inputArgs[0],
        meta: inputArgs[1]
      });
    }
  }
});

const isProduction = process.env.NODE_ENV === 'production';
const logger = new Axe({
  logger: isProduction ? pino : consola
});

logger.info('hello world');

Silent Logging

Silent logging is useful when you need to disable logging in certain environments for privacy reasons or to simply clean up output on stdout.

For example when you're running tests you can set logger.config.silent = true.

const Axe = require('axe');

const logger = new Axe({ silent: true });

logger.info('hello world');

Stack Traces and Error Handling

Please see Cabin's documentation for stack traces and error handling for more information.

If you're not using cabin, you can simply replace instances of the word cabin with axe in the documentation examples linked above.

Hooks

You can add synchronous "pre" hooks and/or asynchronous/synchronous "post" hooks with Axe. Both pre and post hooks accept four arguments (level, err, message, and meta). Pre hooks are required to be synchronous.

Both pre and post hooks execute serially – and while pre hooks are blocking, post-hooks will run in the background after logger methods are invoked (you can have a post hook that's a Promise or async function).

Pre hooks require an Array to be returned of [ err, message, meta ].

Pre hooks allow you to manipulate the arguments err, message, and meta that are passed to the internal logger methods. This is useful for masking sensitive data or doing additional custom logic before writing logs.

Post hooks are useful if you want to send logging information to a third-party, store them into a database, or do any sort of custom processing.

You should properly handle any errors in your pre hooks, otherwise they will be thrown and logger methods will not be invoked.

We will catch errors for post hooks by default and log them as errors with your logger methods' logger.error method).

Hooks can be defined in the options passed to an instance of Axe, e.g. new Axe({ hooks: { pre: [ fn ], post: [ fn ] } }); and/or with the method logger.pre(level, fn) or logger.post(level, fn). Here are a few examples below:

const Axe = require('axe');

const logger = new Axe({
  hooks: {
    pre: [
      function (level, err, message, meta) {
        message = message.replace(/world/gi, 'planet earth');
        return [err, message, meta];
      }
    ]
  }
});

logger.info('hello world');

// hello planet earth

const Axe = require('axe');

const logger = new Axe();

logger.pre('error', (err, message, meta) => {
  if (err instanceof Error) err.is_beep_boop = true;
  return [err, message, meta];
});

logger.error(new Error('oops'));

// Error: oops
//     at Object.<anonymous> (/Users/user/Projects/axe/test.js:39:14)
//     at Module._compile (node:internal/modules/cjs/loader:1105:14)
//     at Object.Module._extensions..js (node:internal/modules/cjs/loader:1159:10)
//     at Module.load (node:internal/modules/cjs/loader:981:32)
//     at Function.Module._load (node:internal/modules/cjs/loader:822:12)
//     at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:77:12)
//     at node:internal/main/run_main_module:17:47 {
//   is_beep_boop: true
// }

For more examples of hooks, see our below sections on Send Logs to HTTP Endpoint, Send Logs to Slack), and Suppress Logger Data below.

Remapping

If you would like to remap fields, such as response.headers to responseHeaders, then you can use environment variables or pass an object with configuration mapping.

const logger = new Axe({
  meta: {
    remappedFields: {
      'response.headers': 'responseHeaders'
    }
  }
});

logger.info('foo bar', {
  response: {
    headers: {
      'X-Hello-World': true
    }
  }
});

// foo bar { responseHeaders: { 'X-Hello-World': true } }

Omitting

If you would like to omit fields, such as response.headers from a response, so you are only left with the status code:

const logger = new Axe({
  meta: {
    omittedFields: ['level', 'err', 'app', 'args', 'response.headers']
  }
});

logger.info('foo bar', {
  response: {
    status: 200,
    headers: {
      'X-Hello-World': true
    }
  }
});

// foo bar { response: { status: 200 } }

Picking

If you would like to pick certain fields, such as response.status from a response:

const logger = new Axe({
  meta: {
    pickedFields: [ 'response.status' ]
  }
});

logger.info('foo bar', {
  response: {
    status: 200,
    headers: {
      'X-Hello-World': true
    }
  }
});

// foo bar { response: { status: 200 } }

Aliases

We have provided helper/safety aliases for logger.warn and logger.error of logger.warning and logger.err respectively.

Methods

A few extra methods are available, which were inspired by Slack's logger and added for compatibility:

• logger.setLevel(level) - sets the log level (String) severity to invoke logger methods for (must be valid enumerable level)
• logger.getNormalizedLevel(level) - gets the normalized log level (String) severity (normalizes to known logger levels, e.g. "warning" => "warn", "err" => "error", "log" => "info")
• logger.setName(name) - sets the name (String) property (some loggers like pino will prefix logs with the name set here)

Examples

Send Logs to HTTP Endpoint

This is an example of using hooks to send a POST request to an HTTP endpoint with logs of the "fatal" and "error" levels that occur in your application:

We recommend superagent, however there are plenty of alternatives such as axios and ky.

1. You will need to install the superagent, cuid, and fast-safe-stringify packages:

   npm install superagent cuid fast-safe-stringify

2. Implementation example is provided below:

   const os = require('os');
   
   const Axe = require('axe');
   const superagent = require('superagent');
   const cuid = require('cuid');
   const safeStringify = require('fast-safe-stringify');
   
   // create our application logger that uses hooks
   const logger = new Axe({
     logger: console, // optional (e.g. pino, signale, consola),
     level: 'info', // optional (defaults to info)
     name: process.env.HOSTNAME || os.hostname() // optional
   });
   
   async function hook(next, message, meta) {
     //
     // return early if we wish to ignore this
     // (this prevents recursion; see end of this fn)
     //
     if (meta.ignore_emit) return next();
   
     try {
       //
       // set the body used in the HTTP request to be consistent object with
       // two properties sent in the payload of `message` and `meta`
       // (and also remove circular references)
       //
       const body = safeStringify({ message, meta });
   
       //
       // send to Cabin or your own custom endpoint here
       // https://cabinjs.com
       //
       const request = superagent
         .post('https://api.cabinjs.com')
         .set('X-Request-Id', cuid()) // normalize server/browser request id formatting
         .timeout(5000);
   
       request.set('User-Agent', `axe/${logger.version}`);
   
       // add basic auth header (e.g. if you use Cabin)
       // if (config.key) request.auth('INSERT-YOUR-KEY');
   
       // set any additional headers if necessary
       // request.set({ ... });
   
       const response = await request
         .type('application/json')
         .retry(3)
         .send(body);
   
       logger.info('log sent over HTTP', { response });
     } catch (err) {
       logger.fatal(err, { ignore_emit: true });
     }
   
     // move along to the next hook
     next();
   }
   
   // bind custom hooks for "fatal" and "error" log levels
   logger.post('error', hook);
   logger.post('fatal', hook);
   
   // test out the HTTP integration
   logger.error(new Error('Uh oh something went wrong!'));

Send Logs to Slack

This is an example of using hooks to send a message to Slack with logs of the "fatal" and "error" levels that occur in your application:

1. You will need to install the @slack/web-api package locally:

   npm install @slack/web-api

2. Create and copy to your clipboard a new Slack bot token at https://my.slack.com/services/new/bot.

3. Implementation example is provided below:

   Replace INSERT-YOUR-TOKEN with the token in your clipboard

   const os = require('os');
   
   const Axe = require('axe');
   const { WebClient } = require('@slack/web-api');
   
   // create our application logger that uses hooks
   const logger = new Axe({
     logger: console, // optional (e.g. pino, signale, consola)
     level: 'info', // optional (defaults to info)
     name: process.env.HOSTNAME || os.hostname() // optional
   });
   
   // create an instance of the Slack Web Client API for posting messages
   const web = new WebClient('INSERT-YOUR-TOKEN', {
     // <https://slack.dev/node-slack-sdk/web-api#logging>
     logger,
     logLevel: logger.config.level
   });
   
   async function hook(next, message, meta) {
     //
     // return early if we wish to ignore this
     // (this prevents recursion; see end of this fn)
     //
     if (meta.ignore_emit) return next();
   
     // otherwise post a message to the slack channel
     try {
       const result = await web.chat.postMessage({
         channel: 'monitoring',
         username: 'Axe',
         icon_emoji: '🪓',
         attachments: [
           {
             title: meta.err && meta.err.message ? meta.err.message : message,
             color: 'danger',
             text: meta.err && meta.err.stack ? meta.err.stack : null,
             fields: [
               {
                 title: 'Level',
                 value: meta.level,
                 short: true
               },
               {
                 title: 'Environment',
                 value: meta.app.environment,
                 short: true
               },
               {
                 title: 'Hostname',
                 value: meta.app.hostname,
                 short: true
               },
               {
                 title: 'Hash',
                 value: meta.app.hash,
                 short: true
               }
             ]
           }
         ]
       });
   
       // finally log the result from slack
       logger.info('slack message sent', { result });
     } catch (err) {
       logger.fatal(err, { ignore_emit: true });
     }
   
     // move along to the next hook
     next();
   }
   
   // bind custom hooks for "fatal" and "error" log levels
   logger.post('error', hook);
   logger.post('fatal', hook);
   
   // test out the slack integration
   logger.error(new Error('Uh oh something went wrong!'));

Suppress Logger Data

This is an example of using a custom hook to manipulate logger arguments to suppress sensitive data.

const Axe = require('.');

const logger = new Axe();

for (const level of logger.config.levels) {
  const fn = logger.config.logger[level];
  logger.config.logger[level] = function (message, meta) {
    // replace any messages "beep" -> "boop"
    if (typeof message === 'string') message = message.replace(/beep/g, 'boop');

    // mask the property "beep" in the meta object "data"
    if (meta?.data?.beep)
      meta.data.beep = Array.from({ length: meta.data.beep.length })
        .fill('*')
        .join('');

    return Reflect.apply(fn, this, [message, meta]);
  };
}

logger.warn('hello world beep');

// hello world boop

logger.info('start', {
  data: {
    foo: 'bar',
    beep: 'boop' // <--- we're suppressing "beep" -> "****"
  }
});

// start { data: { foo: 'bar', beep: '****' } }

logger.error(new Error('oops!'), {
  data: {
    beep: 'beep-boop-beep' // this becomes "**************"
  }
});

// Error: oops!
//     at Object.<anonymous> (/Users/user/Projects/axe/test.js:30:14)
//     at Module._compile (node:internal/modules/cjs/loader:1105:14)
//     at Object.Module._extensions..js (node:internal/modules/cjs/loader:1159:10)
//     at Module.load (node:internal/modules/cjs/loader:981:32)
//     at Function.Module._load (node:internal/modules/cjs/loader:822:12)
//     at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:77:12)
//     at node:internal/main/run_main_module:17:47 { data: { beep: '**************' } }

Contributors

License

MIT © Nick Baugh