travix-logger

travix-logger

Logger library for the browser and node.js

• Installation
• Usage
• Guide
  • Levels
  • Transports
  • Formatters
• API
  • Logger
  • createTransport
• Built-in transports
  • Console
  • Http

Installation

Install it via npm:

$ npm install --save travix-logger

Usage

Example usage in ES6 (in node.js and webpack/browserify bundles):

import { Logger, configureConsoleTransport } from 'travix-logger';

const logger = new Logger({
  transports: [
    configureConsoleTransport()
  ]
});

logger.log('Error', 'EventName', 'Some error occurred', { meta: 'values' });

// same as
logger.error('EventName', 'Some error occurred', { meta: 'values' });

In the browser:

<script src="https://unpkg.com/travix-logger@latest/dist/travix-logger.min.js"></script>

<script>
  // now available as `window.TravixLogger`
</script>

---

Guide

Levels

Levels are type of logs that you can capture with travix-logger. If you have a warn level, it will be made accessible to you from the Logger instance as logger.warn(event, message, meta) for example.

By default, these levels are used:

debug

debug(event, message, meta)

Level name: Debug.

info

info(event, message, meta)

Level name: Info.

warn

warn(event, message, meta)

Level name: Warning.

error

error(event, message, meta)

Level name: Error.

exception

exception(event, errorObject, message, meta)

Level name: Error.

Custom levels

You can override the levels data, at Logger instance level as follows:

import { Logger } from 'travix-logger';

const logger = new Logger({
  levels: {
    // key is the method name
    error: {
      name: 'Error' // the level name passed to formatters and transports
    },
    warn: {
      // if `methodName` is not present, it will default to the key `warn`
    },
    exception: {
      error: true // method then accepts `(event, errorObject, message, meta)`
    }
  }
});

Transports

Transports are responsible for storing the logs. Each instance of Logger can have multiple transports. For example, one Transport can be responsible for printing out the logs in console, while the other can sent it to a remote server.

This library already ships with a ConsoleTransport by default, which can be used right away:

import { Logger, configureConsoleTransport } from 'travix-logger';

const logger = new Logger({
  transports: [
    configureConsoleTransport()
  ]
});

Whenever you call logger.log() for example, the ConsoleTransport would take up the responsibility of printing out the log to console every time.

Custom transport

Creating custom transports is very easy, and the library already comes with the necesasry utilities for you:

// ./transports/MyCustomTransport.js

import { createTransport } from 'travix-logger';

export default createTransport({
  initialize() {
    // you have access to Logger instance as `this.logger`.
  },

  log(level, event, message, meta, cb) {
    // do something with the data
    console.log(level, event, message, meta);

    // trigger the callback, when successful
    cb(null);

    // if any error while processing the log
    cb(new Error('Something went wrong while processing the log'));
  }
});

Now you can pass it as a Transport while instantiating a new Logger instance:

import { Logger } from 'travix-logger';
import MyCustomTransport from './transports/MyCustomTransport';

const logger = new Logger({
  transports: [
    MyCustomTransport
  ]
});

Formatters

Formatters can intercept your log data, and modify them before they are sent to Transports.

Custom formatter

They are just plain synchronous functions, which accept the same arguments as Logger.log(), and returns the modified values.

import { Logger } from 'travix-logger';

function myCustomFormatter(level, event, message, meta) {
  meta.addedNewKey = 'some value';

  if (meta.creditCardNumber) {
    meta.creditCardNumber = mask(meta.creditCardNumber);
  }

  message += ' [appended message]';

  return {
    level,
    event,
    message,
    meta
  };
}

const logger = new Logger({
  formatters: [
    myCustomFormatter
  ]
});

---

API

Logger

Constructor options

levels

(optional) Levels object, where level name is the key.

transports

Array of Transport classes.

formatters

Array of Formatter functions.

defaultMeta

(optional) Default meta object that logs' meta will extend from.

timestamp

Defaults to false. When true, it will add a new Date object to the timestamp key in meta object for every new logs.

If you want the timestamp in meta with a different key, you can pass a string instead.

errorMessageKey

For mapping Error.message value in meta, when logging exceptions. Defaults to exceptionmessage.

errorStackKey

For mapping Error.stack value in meta, when logging exceptions. Defaults to exceptiondetails.

Properties

options

Options passed during construction.

Methods

In addition to the methods listed below, Logger instances will also have methods according to the levels.

log

log(level, event, message, meta = {}, logCallback = null)

createTransport

createTransport(options = {})

Options

initialize

initialize()

Called when the Tranport class is constructed.

log

log(level, event, message, meta, cb)

This method must be implemented when creating a new Transport.

If there is any issue while processing the log, call cb(new Error('something went wrong')).

Otherwise, call cb(null);

name

Custom name for the Transport class, defaults to Transport.

Properties

logger

Reference to the parent Logger instance.

each

each(arr, iterator, cb)

Utility function for processing an array asynchronously.

Arguments

1. arr (Array): Array to iterate
2. iterator (Function): Accepting these arguments:
   1. item: The iterated item from the array
   2. cb (Function): Call cb(null) when processed successfully, otherwise call cb(err).
3. cb (Function): Called with null when all items processed successfully, otherwise with err.

---

Built-in transports

Console

A configureable ConsoleTransport is shipped with the package:

import { Logger, configureConsoleTransport } from 'travix-logger';

const logger = new Logger({
  transports: [
    configureConsoleTransport({
      // you can optionally override the `console` function
      console: myAwesomeConsoleObject
    })
  ]
});

Options

console

Unless any function is provided here, it will default to the global scope's console object. Like window.console in the browser.

filter

Optional function that filters the logs from being processed. Defaults to returning true for all logs.

Example:

function filter(level, event, message, meta) {
  return true;
}

format

Optional function that can customize log string in a console.

Example:

function format(level, event, message, meta) {
  return `${level} - ${message}`;
}

name

Defaults to ConsoleTransport.

Http

Transport for sending log data to a remote location:

import { Logger, configureHttpTransport } from 'travix-logger';

const logger = new Logger({
  transports: [
    configureHttpTransport({
      // required
      url: 'https://logs.example.com/submit',

      // optional
      method: 'POST',
      formatBody(level, event, message, meta) {
        return JSON.stringify({
          level,
          message,
          ...meta
        });
      }
    })
  ]
})

Options

url

URL to send the log data to.

filter

Optional function that filters the logs from being processed. Defaults to returning true for all logs.

Example:

function filter(level, event, message, meta) {
  return true;
}

method

One of the HTTP methods, defaults to POST.

GET and HEAD are not allowed, since they do not support body.

name

Defaults to HttpTransport.

eventKey

For mapping the event name in the body. Defaults to messagetype.

formatBody

A function accepting (level, message, meta), and returning a string to be used as body value.

headers

Follows fetch API. Currently defaults to:

{
  'Accept': 'application/json',
  'Content-Type': 'application/json'
}

Other fetch API options

Supports:

• credentials
• mode
• cache
• redirect
• referrer
• referrerPolicy
• integrity

See Fetch API documentation.

---

Release

To release a new version:

$ make release VERSION=patch

VERSION value can be patch, minor, or major following semver.

License

MIT © Travix International