Vue-logger-plugin NPM

vue-logger-plugin

Flexible logging functionality for Vue.js with support for custom hook operations.

Note: Versions 2.x support Vue 3 and versions 1.x support Vue 2. For documentation related to Vue 2, view a 1.x tag

NPM Package Install

npm i vue-logger-plugin

Vue Plugin Install

The logging implementation can be installed by creating a logger instance using createlogger and providing that logger instance to the Vue App.use method.

Here is the simplest usage:

main.js

import { createApp, h } from 'vue';
import { createLogger } from 'vue-logger-plugin'
import App from './App.vue'
createApp({
  render: () => h(App)
})
  .use((createLogger({}))
  .mount('#app')

Doing the above will install the logger with the basic default options.

For advanced usage (i.e. using conditional options and hooks), it is recommended to export the constructed logger instance in a separate file and then import into your main file.

logger/index.js

import { createLogger } from 'vue-logger-plugin'

// create logger with options
const logger = createLogger({
  enabled: true,
  level: 'debug',
  beforeHooks: [ ... ],
  afterHooks: [ ... ]
})

export default logger

main.js

// ...
import logger from './logger'
createApp({
  render: () => h(App)
})
  .use(logger)
  .mount('#app')

More information about hooks can be found in the Hooks section.

Options

(default values shown)

{
  enabled: true,    // {boolean} enable/disable logging
  level: 'debug',   // {string} the logging level (one of: debug, info, warn, error)
  beforeHooks: [],  // {LoggerHook[]} hooks invoked before a statement is logged, can be used to alter log arguments (use carefully)
  afterHooks: []    // {LoggerHook[]} hooks invoked after a statement is logged
}

Hooks

Hooks allow for advanced customization of the logger implementation, providing operations to be run before and after logging is performed. These are defined on options as beforeHooks and afterHooks.

beforeHooks

Invoked before a statement is logged, can alter the log arguments which can impact the log output.

afterHooks

Invoked after a statement is logged, cannot impact the log output.

Built-in Hooks

The following hooks are available in this package and can be used by simply importing and adding them to the beforeHooks and/or afterHooks arrays of your options.

StringifyObjectsHook Applies JSON.stringify on all objects provided as arguments to a logging method.

import { createLogger, StringifyObjectsHook } from 'vue-logger-plugin'
const logger = createLogger({
  // ... (other options)
  beforeHooks: [
    StringifyObjectsHook
  ]
})

StringifyAndParseObjectsHook Applies JSON.stringify and JSON.parse on all objects provided as arguments to a logging method.

import { createLogger, StringifyAndParseObjectsHook } from 'vue-logger-plugin'
const logger = createLogger({
  // ... (other options)
  beforeHooks: [
    StringifyAndParseObjectsHook
  ]
})

The above are best used as 'before hooks' as they may purposefully alter the log output. This way you are sure you are seeing the value of an object at the moment you log it. Otherwise, many browsers provide a live view that constantly updates as values change.

Write Your Own Hooks

You can easily write your own hooks to apply custom logic. A hook must implement a run function to handle a log event (an object containing the log level and the array of arguments which were passed to the logging method), and may optionally implement an install function which is invoked during plugin installation (or at the time of logger options application - see Usage section).

For reference, here are the interfaces:

export interface LoggerHook {
  run (event: LogEvent): void
  install? (options: LoggerOptions): void
  props?: { [key: string]: any }
}
export interface LogEvent {
  level: string
  argumentArray: any[]
}

Sample Custom Hook - Leveraging Axios to Send Logs to Server

This is a basic example demonstrating how you could have the logger send log data to a server using an Axios client.

logger/index.js

import { createLogger, StringifyObjectsHook } from 'vue-logger-plugin'
import axios from 'axios'

const ServerLogHook = {
  run (event) {
    axios.post('/log', { severity: event.level, data: event.argumentArray })
  }
}

const logger = createLogger({
  // ... (other options)
  beforeHooks: [
    StringifyObjectsHook
  ],
  afterHooks: [
    ServerLogHook
  ]
})

export default logger

logger/index.ts (TypeScript example, same functionality as above)

import { createLogger, StringifyObjectsHook, LoggerHook, LogEvent } from 'vue-logger-plugin'
import axios from 'axios'

const ServerLogHook: LoggerHook = {
  run (event: LogEvent) {
    axios.post('/log', { severity: event.level, data: event.argumentArray })
  }
}

const options: LoggerOptions = {
  // ... (other options)
  beforeHooks: [
    StringifyObjectsHook
  ],
  afterHooks: [
    ServerLogHook
  ]
}

export default logger

Usage

Composition API: Import and use the useLogger method to inject the logger instance.

import { defineComponent } from 'vue'
import { useLogger } from 'vue-logger-plugin'
export default defineComponent({
  name: 'MyComponent',
  setup () {
    const log = useLogger()
    log.info('Setting up MyComponent...')
    return {
      log
    }
  },
  // example logger usage from outside of setup method
  methods: {
    test() {
      const testObject = {
        name: 'test',
        value: 'this is a test object'
      }
      this.log.debug('Test Message', testObject)
      this.log.info('Test Message', testObject)
      this.log.warn('Test Message', testObject)
      this.log.error('Test Message', testObject)
      this.log.log('Test Message', testObject)
      // change options
      this.log.apply({ level: 'error' }) // applies new log level
      this.log.warn('This is not logged now')
    }
  }
})

As described in the Vue Plugin Install section above, options can be provided to the createLogger function for customizing the logging implementation. As well, the logger options can be applied at any time to the logger on the Vue instance via the apply function (as demonstrated in the above example code). This allows for on-demand enabling/disabling of the logger and adjusting log levels as needed from within your components. Any options available to createLogger are also available to the apply function.