quartis.js

function getSizeArray(arr) {
  return arr.lenth
}

function getModule2(arr) {
  let size = getSizeArray(arr)
  return size % 2 == 0
}

function getDivide2(arr) {
  let size = getSizeArray(arr)
  return size / 2
}

function firstQuartil(arr) {
  let module2 = getModule2(arr)
  let div2 = getDivide2(arr)

  return (module2) ? arr.slice(0, (div2)) : arr.slice(0, Math.floor(module2));
}

function thirdQuartil(arr) {
  let module2 = getModule2(arr)
  let div2 = getDivide2(arr)
  let sizeArray = getSizeArray(values)

  return (module2) ? arr.slice((div2), sizeArray) : arr.slice(Math.ceil(div2), sizeArray);
}

function medianX(arr) {
  let count = getSizeArray(arr);
  let module2 = getModule2(arr)
  let module2help = getDivide2(arr[(getDivide2(arr)) - 1] + arr[(getDivide2(arr))])
  let arrDivide2 = arr[Math.floor(getDivide2(2))]

  if (module2) {
    return module2
  } else if (module2help) {
    return module2help
  }

  return arrDivide2
}

test-quartis.js

const values = require('./values')
const q1 = firstQuartil(values)
const q2 = values
const q3 = thirdQuartil(values)

console.log("Quartil 1 25% " + medianX(q1)) //Quartil 1 25% 50.4481202037 
console.log("Quartil 2 50% " + q2) //Quartil 2 50% 41.83728231035
console.log("Quartil 3 75% "+ medianX(q3)) // Quartil 3 75% 82.02411431499999

values.js

values = [
  82.1467068058,
  38.4966734016,
  32.0008188793,
  96.9622650244,
  86.8058759993,
  79.3362306586,
  58.0055852798,
  75.8220414787,
  67.0149545567,
  36.4044706595,
  85.3345320643,
  20.6287894419,
  81.7456373986,
  24.4326880876,
  19.9944876851,
  80.2303362813,
  98.6854373061,
  4.3960766433,
  22.1212283642,
  53.1724684800,
  50.3620960690,
  11.3724002897,
  41.0039978225,
  64.8333473234,
  15.5894909570,
  85.3067494504,
  84.0015994709,
  91.3425614815,
  47.3171987992,
  16.5602177445,
  86.5891620670,
  27.3438542203,
  72.3398157121,
  18.5367692487,
  40.5793436922,
  70.1641373485,
  59.9469967755,
  64.6235988325,
  35.4129698701,
  90.1449361797,
  89.5436831889,
  20.7605480631,
  72.2822633062,
  27.9079298572,
  67.1159466004,
  68.6223243990,
  88.5802505560,
  13.6363037261,
  24.7355830273,
  19.7367890419,
  63.9377755788,
  75.6711643900,
  31.9382648930,
  45.6193707884,
  43.8147543419,
  18.2865472284,
  39.0358874791,
  6.6626381087,
  64.3532950055,
  57.8284906640,
  69.1947236148,
  18.9723704594,
  28.5984494536,
  86.5579189727,
  34.9384562133,
  26.2378601208,
  97.9248087536,
  38.6448350638,
  77.7968509496,
  77.5877098686,
  1.4398382678,
  87.6189498380,
  47.8376225653,
  6.8257593391,
  95.6884705282,
  68.3597581018,
  48.1638241128,
  16.1232389894,
  6.8025946135,
  49.6078329777,
  17.1302162234,
  49.6477608677,
  84.0468898717,
  60.3049364974,
  65.8149959441,
  71.6199402320,
  37.6571363245,
  88.7415553423,
  66.4689612964,
  52.4968718552,
  55.0881701336,
  23.2653091083,
  79.5475241154,
  92.2793432818,
  82.4489210807,
  62.3116121280,
  75.2383286962,
  76.5622551190,
  26.9191521540,
  65.2132617394];