Javascript Object composition, inheritance and private state
Inspired by Composing Software: An Introduction an article on Medium by Eric Elliott
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 ...'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