JS Utility Functions

_Utility.js

function randomNumberBetween(min, max) {
  return Math.floor(Math.random() * (max - min + 1) + min)
}

/**
 * example: sleep(1000).then(() => { ...doSomeThing })
 */
function sleep(duration) {
  return new Promise(resolve => {
    setTimeout(resolve, duration)
  })
}

/**
 * cache method result
 * example: 
 * const add = memoize((a, b) => a + b)
 * add(2, 5) // 7 <- this result is cached
 * add(2, 5) // 7 <- return cached value
 */
function memoize(cb) {
  const cache = new Map()
  return (...args) => {
    const key = JSON.stringify(args)
    if (cache.has(key)) return cache.get(key)
    const result = cb(...args)
    cache.set(key, result)
    return result
  }
}

/**
 * example: 
 * const people = [{ name: "Kyle", age: 18 }, { name: "Mike", age: 18 }, { name: "Jill", age: 26 }]
 * groupBy(people, "age") // { 18: [{ name: "Kyle", age: 18 }, { name: "Mike", age: 18 }], 26: [{ name: "Jill", age: 26 }] }
 */
function groupBy(array, key) {
  return array.reduce((group, element) => {
    const keyValue = element[key]
    return { ...group, [keyValue]: [...(group[keyValue] ?? []), element] }
  }, {})
}

const DIVISIONS = [
  { amount: 60, name: "seconds" },
  { amount: 60, name: "minutes" },
  { amount: 24, name: "hours" },
  { amount: 7, name: "days" },
  { amount: 4.34524, name: "weeks" },
  { amount: 12, name: "months" },
  { amount: Number.POSITIVE_INFINITY, name: "years" },
]
// locale "undefined" use environment(browser) default language, or specific like "en", "ja"
const RELATIVE_DATE_FORMATTER = new Intl.RelativeTimeFormat(undefined, { numeric: "auto" })
/**
 * example: 
 * formatRelativeDate(new Date(new Date().setDate(25))) // 'in 3 weeks'
 * formatRelativeDate(new Date(new Date().setDate(-25))) // '4 weeks ago'
 */
function formatRelativeDate(toDate, fromDate = new Date()) {
  let duration = (toDate - fromDate) / 1000
  for (let i = 0; i <= DIVISIONS.length; i++) {
    const division = DIVISIONS[i]
    if (Math.abs(duration) < division.amount) {
      return RELATIVE_DATE_FORMATTER.format(Math.round(duration), division.name)
    }
    duration /= division.amount
  }
}