mix-in

Turns a set of functions into a mix-in/trait that can extend a class.

Installation

Requires Node.js 7.0.0 or above.

npm i mix-in

Basic Usage

Step 1: Define the Mix-In

Let’s say you want to create a module that adds enable() and disable() methods to a class. Your module would require('mix-in') and look like this:

const Mixin = require('mix-in')

module.exports = Mixin({
  enable () {
    // TODO
  },

  disable () {
    // TODO
  },
})

This is all you need to do for your mix-in module. Easy enough, right? Now we’ll turn to the module that makes use of your new mix-in.

Step 2: Require and Apply the Mix-In

Let’s say you have a second module that exports a Button class and you want to extend it with your mix-in module from step 1, which you named @lamansky/enable-disable-mix-in.

module.exports = class Button {
  // Methods go here
}

All you have to do in the dependent module is:

1. Require the mix-in.
2. Call it as a function without arguments.
3. Call it again, passing the class as an argument.

Like so:

// Note the function call at the end of this line; you need to have that!
const EnableDisable = require('@lamansky/enable-disable-mix-in')()

module.exports = EnableDisable(class Button {
  // This class now has enable() and disable() methods!
})

That’s it! Your Button class prototype now has enable() and disable() methods.

Advanced Usage: Parameters

You can also create mix-ins that accept arguments. This is useful for creating configurable mix-ins, or mix-ins that access private properties using symbols.

Step 1: Define the Mix-In

Instead of defining your mix-in as an object, we’ll create a function that takes arguments. Let’s modify our previous mix-in so that it makes use of a symbol:

const Mixin = require('mix-in')

module.exports = Mixin(_enabled => ({
  enable () {
    this[_enabled] = true
  },

  disable () {
    this[_enabled] = false
  },
}))

Step 2: Require and Apply the Mix-In

Now do the following in the dependent module:

1. Require the mix-in.
2. Call it as a function, passing the arguments your mix-in is expecting.
3. Call it again, passing the class as an argument.

const _enabled = Symbol('enabled')
const EnableDisable = require('@lamansky/enable-disable-mix-in')(_enabled)

module.exports = EnableDisable(class Button {
})

Just like before, your Button now has enable() and disable() in its prototype, except this time, both your Button class and your mix-in have access to the same _enabled symbol.