Bean

Javascript Object composition, inheritance and private state

Inspired by Composing Software: An Introduction an article on Medium by Eric Elliott

Basic Usage

Bean.roast returns a function that is used as a factory of Javascript objects. It takes as first parameter an optinal constructor and a series of object that will be composed into the final prototype and descriptors.

    const Bean = require('bean')
    
    const Character = Object.create({
      whoami() {
        return `a bat called ${this.name || '...'}`
      },
    })

    const FlyingThing = Object.create({
      canFly: true,
      fly() {
        return 'flap, flap ...'
      }
    })

    const Duck = Bean.roast(
      function Duck(name) {
        this.name = name
        this.specie = 'bird'
      },
      Character,
      FlyingThing
    )

    const Bat = Bean.roast(
      function Bat(name) {
        this.name = name
        this.specie = 'mammal'
      },
      Character,
      FlyingThing
    )

    const Dog = Bean.roast(
      function Dog(name) {
        this.name = name
        this.specie = 'mammal'
      },
      Character
    )

    const daffyDuck = Duck('Daffy Duck')

In a console:

    daffyDuck
    > Duck { name: 'Daffy Duck', specie: 'bird' }
    daffyDuck.fly()
    > 'flap, flap ...'

Private State

Bean.wrap is a function, enabled by module wrap-bean, that wraps a context arround bean creation.

    const Bean = require('../src/bean')
    require('bean/wrap-bean') // enable Bean.wrap function
    module.exports = Bean.wrap(() => {
      // wrapping this implementation, not exposing it
      // this implementation takes care of optimising caching...
      const PrimeIndex = Bean.roast(
        function PrimeIndex() { ... }, Bean.protected({
          set(prime, seq) { ... },
          test(candidate) { ... },
          next(treshold) { ... },
        }), {
          // properties
          ...
        }
      )
      // Private constant that is not exposed
      const primeIndex = PrimeIndex()
      // Only exposing this bean
      // Exposing this bean
      return Bean.roast(
        // cosmetic construcor - looks nice this the console
        function Prime() {},
        Bean.protected({
          /**
           * test whether a candidate integer is a prime number
           * @param {Integer} candidate 
           */
          test(candidate) {
            return primeIndex.test(candidate)
          },
          /**
           * Retreive a given number of prime numbers
           * @param {Integer} length number of prime number to return
           */
          getList(length) {
            while (primeIndex.sequence.length < length) {
              primeIndex.next(+Infinity)
            }
            return primeIndex.sequence.slice(0, length)
          }
        })
      )
    })

Check test/wrap-bean.js for more examples