Babel Plugin Console Log

A babel plugin for enhanced console logging behavior in browsers.

This plugin does not make any changes to the actual console object. It simply provides convenience methods available in your development source files. The transformed output effects the aspects such as the arguments that are passed to the console methods.

Thanks to the meaningful logs plugin for inspiration!

What problem does this plugin solve?

One of the primary disadvantages of using a client-side logging framework is that the original source file name and line number are not properly displayed in the console. This is because the logging frameworks create a wrapper around the actual console.log call, making it appear that all logs originated from the same location within the logging wrapper. This wrapper is typically necessary when any sort of dynamic processing is to take place.

Some logging frameworks, such as loglevel, are able to retain the correct source file and line number by building logger functions that have been bound to the actual console commands. Unfortunately, there are significant limitations to this approach since it is still not possible to perform any dynamic changes at runtime. In fact, try using any loglevel plugin and you no longer get accurate line number reporting.

Instead babel-plugin-console-log transforms calls to console methods at build time. This enables developers to have a simple and clean logging API that gets converted to more complex console statements behind-the-scenes. When used in conjunction with a client-side logging framework such as loglevel, much more dynamic processing is possible without the drawbacks.

What can you do with this plugin?

At this early stage of development, this plugin can be used to add effects such as color and font size changes to your console output. It can be used with both console logging as well as any logging framework the user would like to use, such as loglevel, winston, bunyan, etc.

As it is further developed, far more capabilities are anticipated. See below for a list of future enhancements. These include prefixing logs with log level and module information, adding timestamps, labeling arguments, grouping arguments, and more.

How does it work?

This babel plugin simply takes your development source and looks for AST nodes that match any configured loggers (console by default). If the method called on that logger matches a registered effect, then the output gets transformed as specified by that effect.

Installation

npm install --save-dev babel-plugin-console-log

Configuration

Loggers

By default, this plugin adds effects to the console logger. But it can be customized to other loggers. For instance, to add effects to the winston logger instead of the console, you would put this in your .babelrc file:

{
  "plugins": [
    [ "console-log", { "loggers": [{ "pattern": "winston" }] } ]
  ]
}

If you wanted effects to work on both console and a loglevel log instance:

{
  "plugins": [
    [ "console-log", { "loggers": [
      { "pattern": "console" },
      { "pattern": "log", "method": "trace" }
    ] } ]
  ]
}

The default method for loggers is log. In other words, when the plugin configuration for an effect does not specify a method, console.log will be used (or log.log, etc.). This can be overridden on a per-logger basis. For instance, loglevel does not have a log.log method, so specifying trace will instead use log.trace.

Default Effects

This plugin adds convenience effects to the console object for use in your development source files. It does not actually change the real console object in any way. The following default effects are included:

• the colors defined in lib/colors.js
• the background colors defined in lib/colors.js
• the sizes defined in lib/sizes.js
• additional built-in effects defined in lib/effects.js

Default effects can be used to colorize or change the font size of logged output. For instance:

console.green('I am green')
console.large('I am large')
console.bgsilver('I have a silver background')
console.highlight('I am highlight')

transforms to:

console.log('%cI am green', 'color: green')
console.log('%cI am large', 'font-size: large')
console.log('%cI have a silver background', 'background-color: silver')
console.log('%cI am highlight', 'background-color: yellow; font-size: medium')

Note that at this time, only one effect may be used, you cannot chain multiple effects. But this is an enhancement that would be great to have. Feel free to contribute!

Also, effects only work when the first argument is a string or template literal. If the first argument is a number, a boolean, an expression, or anything else, the effect is not applied to the log output.

Custom Effects

Users can create custom effects as well as override default effects. Standard console commands can also have effects applied to them. Custom effects can leverage multiple default effects or any styles you wish to include.

{
  plugins: [
    [
      'console-log',
      { 
        effects: [
          { 
            // Custom effect name
            pattern: 'bigblue',
            // Explicitly list styles
            styles: 'font-size: x-large; color: blue'
          },
          { 
            // Custom effect name
            pattern: 'tinyred',
            // Use console.warn instead of console.log
            method: 'warn',
            // Combine styles from other effects
            effects: [ 'xxsmall', 'red' ]
          },
          { 
            // Add effect to built-in console method
            pattern: 'debug',
            // Combine styles from other effects
            effects: [ 'red', 'xlarge' ],
            // Add addtional styles
            styles: 'padding: 3px; font-weight: bold'
          } 
        ] 
      }
    ]
  ]
}

These could then be used like this:

console.bigblue("Big and blue")
console.tinyred("Tiny and red and ouput using console.warn")
console.debug("Big and red and bold with padding")

See test/main.js for more examples.

Possible Future Enhancements

The following are features that could be added to this plugin. If any of these interest you, please contribute to the project!

Combine multiple effects

console.yellow.bggrey.xlarge('I am extra large yellow text with grey background')

Prefix templates

import loglevel from 'loglevel'
const log = loglevel.getLogger('mymodule')
log.debug("Should add prefixed information")

Transforms to:

import loglevel from 'loglevel'
const log = loglevel.getLogger('mymodule')
log.debug(`[${log.getLevel()}:${log.getName()}] Should add prefixed information`)

Note that Loglevel currently doesn't have a getName() method.

The loglevel-message-prefix plugin may prove useful.

Timestamp in templates

console.log("Include a timestamp")

Transforms to:

console.log(`[${(new Date()).toLocaleTimeString()}] Include a timestamp`)

Argument labeling

console.log(firstname, lastname, city)
console.log(a < 10, items[0])

Transforms to:

console.log("firstname, lastname, city", firstname, lastname, city)
console.log("a < 10, items[0]", a < 10, items[0])

See meaningful logs plugin for inspiration.

Auto-grouping

console.warn("User info collapsed", user, currentState, idx)
 
console.log.expanded("Project info expanded", project, currentState, idx)

Transforms to:

console.groupCollapsed("%cUser info collapsed", "background-color: #FFFAE0; font-weight: normal; padding: 3px")
console.warn("user", user)
console.warn("currentState", currentState)
console.warn("idx", idx)
console.groupEnd()
 
console.group("Project info expanded")
console.log("project", project)
console.log("currentState", currentState)
console.log("idx", idx)
console.groupEnd()

Logging Service Integration

console.log('Print me and also sent me to remote service')

Tranforms to:

console.log('Print me and also sent me to remote service')
remoteService.log('Print me and also sent me to remote service')

Contributing

• Fork & clone locally
• Add tests
• Implement feature
• Make sure all tests pass npm run build; npm test
• Create PR request (only ONE new feature per PR)