habits.ts

import * as fs from 'fs/promises'
interface Habit {
    name: string
    process: string[]
}

interface HabitsPageDependencies {
    load: (amount: number) => Promise<Habit[]>
}

const loadByFs = (amount: number): Promise<Habit[]> => 
    fs.readFile('my-habits.json')
        .then(f => f.toString())
        .then(JSON.parse)
        .then((h: Habit[]) => h.slice(0, amount))

const HabitsPage = (dependencies: HabitsPageDependencies) => ({
    getAllHabits: () => dependencies.load(5000)
})

const slowHabitsPage = HabitsPage({
    load: loadByFs
})

slowHabitsPage.getAllHabits() // always loads file

import * as R from 'ramda'

const memoizedHabitsPage = HabitsPage({
    load: R.memoizeWith((amount: number) => amount + '', loadByFs)
})