Node.js Plug-And-Play package

Easily create hooks and let users plug their own logic across your code to make it extensible by everyone with new features.

Main features

• Extention points definition
  Simple to declare new extention points, yet a lot of flexibility to the plugin authors.
• Hook definition
  Plugin writer can intercept calls to a function by placing their own logicl before, after and even switching the default implementation.
• Dependency management
  Plugins can require other plugins as required dependencies as well as choose the order of execution of each hook.
• Promise support
  Hook can be synchronous and asynchronous when returning a promise.
• Nested/hierachical
  Instanciate plugin instances with a parent reference and parent hooks will also be available inside the children.

Learning

We encourage your to read the detailed tutorial on how to create a plugin architected with Plug and Play published by Adaltas.

Quick example

Library and application authors must define hooks, see ./sample/lib.js:

const plugandplay = require('plug-and-play')

const plugins = plugandplay()

module.exports = {
  // Create and export a new Plug and Play instance
  plugins: plugins,
  // Our core library function
  print: function() {
    // Wrap-up code
    plugins.call({
      // Identify this hook with a name
      name: 'hooks:print',
      // Expose arguments to plugins authors
      args: {
        data: { message: 'hello' }
      },
      // Default implementation
      handler: ({data}) => {
        // Original library
        console.log(data.message)
      }
    })
  }
}

Users and pluging authors can now register their own hooks, see ./sample/index.js:

const mysuperlibrary = require('./lib')

mysuperlibrary.plugins.register({
  hooks: {
    'hooks:print': ({data}, handler) => {
      // Alter the argument
      data.message = 'Hello World'
      // Print a message before the library code
      console.log('>>>>>>>>>>>')
      // Call the original handler
      const result = handler.call(null, {data: data})
      // Print a message after the library code
      console.log('<<<<<<<<<<<')
      return result
    }
  }
})
mysuperlibrary.print()

While the original print function was only printing Hello to stdout, the introduction of this new plugin prints:

>>>>>>>>>>>
Hello world
<<<<<<<<<<<

API

The package export a function to create a new instance:

const plugandplay = require('plug-and-play')

const plugins = plugandplay()

It accepts an option object with the properties:

• args ([string])
  Arguments to pass to the plugin when they are instantiated, only apply if the plugin is defined as a function.
• chain (any)
  The value returned by Plug-And-Play register function, default to the Plug-And-Play instance.
• parent (plugandplay)
  A parent instance of Plug-And-Play to inherit plugins from.
• plugins ([plugin])
  List of plugins to register

Plugin object

A plugin is an object literal with the properties:

• hooks ({name: hook})
  List of hooks identified by hook names.
• name (string)
  Name of the plugin.

Alternatively, a plugin can be defined as a function which return the same plugin object and receive the args property from the Plug-And-Play function.

Hook object

A hook is an object literal with the properties:

• after ([string])
  List of plugin names with hook of the same name are to be executed before, a string is coerced to an array.
• name (string)
  The name of the hook.
• before ([string])
  List of plugin names with hook of the same name are to be executed after, a string is coerced to an array.

Note, when referencing plugins with after and before, the plugins do not need to exists. If they do, they are required to export a hook of the same name.

Call function

The function signature is:

call({args = [], handler, hooks = [], name})

Execute a hander function and its associated hooks. The first argument is an object with the properties:

• args (any) The argument pass to the handler function as well as all hook handlers
• handler (function)
  The function to decorate, receive the value assocaited with the args property.
• name (string)
  The plugin hook to refer to.
• hooks ([hook])
  List of completary hooks from the end user.

Get function

The function signature is:

get({name, hooks, sort})

The get function return hooks. It expects a property option which is a literal object with the properties:

• name (string)
  Name of the hook.
• hooks ([hook]) List of completary hooks from the end user.
• sort (boolean)
  Sort the hooks relatively to each other using the after and before properties.

Register function

The function signature is:

register(plugin)

Plugin can be provided when instantiating Plug-And-Play by passing the plugins property or they can be provided later on by calling the register function. The function only accept one argument, the plugin property:

• plugin (plugin)
  A plugin object.

Roadmap

Worth considering: move the name property of get and call into the first argument and move the other properties into a second argument named option.