Partial application and Currying in JavaScript

currying.js

// JavaScript
//
// Partial application
//  prefilling argument
const add = (...args) => [...args].reduce((a, b) => a + b)

const addMore = add.bind(undefined, 3, 5, 10)
console.log('bind addMore(2)', addMore(2)) // bind addMore(2) 20

const mergeObject = (a, b) => Object.freeze({
    ...a,
    ...b,
    keyX: `${a.keyA} ${a.keyB}`,
})
const defaultData = Object.freeze({
    keyA: 'valueA',
    keyB: 'valueB',
    keyC: 'valueC',
})
let data = mergeObject.bind(null, defaultData)
let dataCurrent = Object.freeze(data({
    keyA: 'newValueA',
}))
console.log('bind mergeObject()', dataCurrent)
// bind mergeObject() {
//     keyA: 'newValueA',
//     keyB: 'valueB',
//     keyC: 'valueC',
//     keyX: 'valueA valueB'
//   }


data = mergeObject.bind(null, dataCurrent)
dataCurrent = data({
    keyB: 'newValueB',
})
console.log('bind mergeObject()', dataCurrent)
// bind mergeObject() {
//     keyA: 'newValueA',
//     keyB: 'newValueB',
//     keyC: 'valueC',
//     keyX: 'newValueA valueB'
//   }

//
// Currying
//  Simplify a function by breaking it down into multiple one-argument functions

const curryAdd = (x) => (y) => x + y
console.log('curryAdd(2)(3)', curryAdd(2)(3)) // curryAdd(2)(3) 5


// Currying and Partial application
const curryAddFlex = (x = 0, y = 0) => {
    const total = x + y
    return {
        add: curryAddFlex.bind(null, total),
        done: () => total
    }
}

const cfa = curryAddFlex()
console.log(
    'cfa.add(2).add(4).add(6).add(-4).done()',
    cfa
        .add(2)
        .add(4)
        .add(6)
        .add(-4)
        .done()
) // cfa.add(2).add(4).add(6).add(-4).done() 8
console.log('cfa.add(24).done()', cfa.add(24).done()) // cfa.add(24).done() 24

const cfa2 = curryAddFlex(10)
console.log(cfa2.add(10).add(50).done()) // 70
console.log(cfa2.add(10).done()) // 20
console.log(cfa2.add(10)) // { add: [Function: bound curryAddFlex], done: [Function: done] }

const iPerson = (data = {
    firstName: undefined,
    lastName: undefined,
}) => {
    const person = {
        data,
    }
    const updateFirstName = (person, name) => {
        person.data.firstName = name
        return person
    }
    const updateLastName = (person, name) => {
        person.data.lastName = name
        return person
    }

    person.setFirstName = updateFirstName.bind(null, person)
    person.setLastName = updateLastName.bind(null, person)
    person.done = () => person.data
    return person
}

const person = iPerson()
console.log(person.done()) // { firstName: undefined, lastName: undefined }
console.log(
    "person().setFirstName('Jon').setLastName('Deo').done()",
    person
        .setFirstName('Jon')
        .setLastName('Deo')
        .done()
) // person().setFirstName('Jon').setLastName('Deo').done() { firstName: 'Jon', lastName: 'Deo' }
console.log(person.setFirstName('Jane').done()) // { firstName: 'Jane', lastName: 'Deo' }


class Person {
    constructor(person = null) {
        const defaultPerson = {
            firstName: undefined,
            lastName: undefined,
        }
        const { firstName, lastName } = { ...person, ...defaultPerson }
        this.firstName = firstName
        this.lastName = lastName
    }

    setFirstName(name) {
        this.firstName = name
        return this
    }

    setLastName(name) {
        this.lastName = name
        return this
    }
}

const myPerson = new Person()
console.log(myPerson) // Person { firstName: undefined, lastName: undefined }
console.log(myPerson.setFirstName('Jon').setLastName('Deo')) // Person { firstName: 'Jon', lastName: 'Deo' }

// Factorial
const range = (a, b) => a > b ? [] : [a, ...range(a + 1, b)]
const multiply = arr => arr.reduce((p, a) => p * a)
const factorial = n => multiply(range(1, n))
console.log(multiply(range(1, 4)), factorial(5)) // 24 120
console.log(factorial(6)) // 720

// Random / Test
function getRandomInt(min, max, random = Math.random) {
    return Math.floor(random() * (max - min)) + min
}

console.log(getRandomInt(0, 10, () => 0.7) === 7) // true
console.log(getRandomInt(0, 10, () => 0.2) === 2) // true

const getInt = getRandomInt.bind(null, 50, 100)
console.log(getInt(() => 0.5)) // 75
console.log(getInt()) // 50-100