Favorite JavaScript Utilities

const castArray = (value) => (Array.isArray(value) ? value : [value]);

// Examples
castArray(1); // [1]
castArray([1, 2, 3]); // [1, 2, 3]

// `arr` is an array
const isEmpty = (arr) => !Array.isArray(arr) || arr.length === 0;

// Examples
isEmpty([]); // true
isEmpty([1, 2, 3]); // false

// `arr` is an array
const clone = (arr) => arr.slice(0);

// Or
const clone = (arr) => [...arr];

// Or
const clone = (arr) => Array.from(arr);

// Or
const clone = (arr) => arr.map((x) => x);

// Or
const clone = (arr) => JSON.parse(JSON.stringify(arr));

// Or
const clone = (arr) => arr.concat([]);

// `a` and `b` are arrays
const isEqual = (a, b) => JSON.stringify(a.sort()) === JSON.stringify(b.sort());

// Examples
isEqual([1, 2, 3], [1, 2, 3]); // true
isEqual([1, 2, 3], [1, 3, 2]); // true
isEqual([1, 2, 3], [1, '2', 3]); // false

// `a` and `b` are arrays
const isEqual = (a, b) => JSON.stringify(a) === JSON.stringify(b);

// Or
const isEqual = (a, b) => a.length === b.length && a.every((v, i) => v === b[i]);

// Examples
isEqual([1, 2, 3], [1, 2, 3]); // true
isEqual([1, 2, 3], [1, '2', 3]); // false

const toObject = (arr, key) => arr.reduce((a, b) => ({ ...a, [b[key]]: b }), {});

// Or
const toObject = (arr, key) => Object.fromEntries(arr.map((it) => [it[key], it]));

// Example
toObject(
    [
        { id: '1', name: 'Alpha', gender: 'Male' },
        { id: '2', name: 'Bravo', gender: 'Male' },
        { id: '3', name: 'Charlie', gender: 'Female' },
    ],
    'id'
);
/* 
{
    '1': { id: '1', name: 'Alpha', gender: 'Male' },
    '2': { id: '2', name: 'Bravo', gender: 'Male' },
    '3': { id: '3', name: 'Charlie', gender: 'Female' },
}
*/

const toNumbers = (arr) => arr.map(Number);

// Or
const toNumbers = (arr) => arr.map((x) => +x);

// Example
toNumbers(['2', '3', '4']); // [2, 3, 4]

const countBy = (arr, prop) => arr.reduce((prev, curr) => ((prev[curr[prop]] = ++prev[curr[prop]] || 1), prev), {});

// Example
countBy(
    [
        { branch: 'audi', model: 'q8', year: '2019' },
        { branch: 'audi', model: 'rs7', year: '2020' },
        { branch: 'ford', model: 'mustang', year: '2019' },
        { branch: 'ford', model: 'explorer', year: '2020' },
        { branch: 'bmw', model: 'x7', year: '2020' },
    ],
    'branch'
);

// { 'audi': 2, 'ford': 2, 'bmw': 1 }

const countOccurrences = (arr, val) => arr.reduce((a, v) => (v === val ? a + 1 : a), 0);

// Or
const countOccurrences = (arr, val) => arr.filter((item) => item === val).length;

// Examples
countOccurrences([2, 1, 3, 3, 2, 3], 2); // 2
countOccurrences(['a', 'b', 'a', 'c', 'a', 'b'], 'a'); // 3

const countOccurrences = (arr) => arr.reduce((prev, curr) => ((prev[curr] = ++prev[curr] || 1), prev), {});

// Examples
countOccurrences([2, 1, 3, 3, 2, 3]); // { '1': 1, '2': 2, '3': 3 }
countOccurrences(['a', 'b', 'a', 'c', 'a', 'b']); // { 'a': 3, 'b': 2, 'c': 1 }

const accumulate = (arr) =>
    arr.map(
        (
            (sum) => (value) =>
                (sum += value)
        )(0)
    );

// Or
const accumulate = (arr) => arr.reduce((a, b, i) => (i === 0 ? [b] : [...a, b + a[i - 1]]), []);

// Or
const accumulate = (arr) => arr.reduce((a, b, i) => (i === 0 ? [b] : [...a, b + a[i - 1]]), 0);

// Example
accumulate([1, 2, 3, 4]); // [1, 3, 6, 10]
// 1             = 1
// 1 + 2         = 3
// 1 + 2 + 3     = 6
// 1 + 2 + 3 + 4 = 10

const range = (min, max) => [...Array(max - min + 1).keys()].map((i) => i + min);

// Or
const range = (min, max) =>
    Array(max - min + 1)
        .fill(0)
        .map((_, i) => min + i);

// Or
const range = (min, max) => Array.from({ length: max - min + 1 }, (_, i) => min + i);

// Example
range(5, 10); // [5, 6, 7, 8, 9, 10]

const cartesian = (...sets) => sets.reduce((acc, set) => acc.flatMap((x) => set.map((y) => [...x, y])), [[]]);

// Example
cartesian([1, 2], [3, 4]); // [ [1, 3], [1, 4], [2, 3], [2, 4] ]

/*
       3       4
   ---------------
1 | [1, 3]  [1, 4]
  |
2 | [2, 3]  [2, 4]

*/

const empty = (arr) => (arr.length = 0);

// Or
arr = [];

// Find the number from `arr` which is closest to `n`
const closest = (arr, n) => arr.reduce((prev, curr) => (Math.abs(curr - n) < Math.abs(prev - n) ? curr : prev));

// Or
const closest = (arr, n) => arr.sort((a, b) => Math.abs(a - n) - Math.abs(b - n))[0];

// Example
closest([29, 87, 8, 78, 97, 20, 75, 33, 24, 17], 50); // 33

const lastIndex = (arr, predicate) => arr.reduce((prev, curr, index) => (predicate(curr) ? index : prev), -1);

// Or
const lastIndex = (arr, predicate) => arr.map((item) => predicate(item)).lastIndexOf(true);

// Example
lastIndex([1, 3, 5, 7, 9, 2, 4, 6, 8], (i) => i % 2 === 1); // 4
lastIndex([1, 3, 5, 7, 9, 8, 6, 4, 2], (i) => i > 6); // 5

const indexOfMax = (arr) => arr.reduce((prev, curr, i, a) => (curr > a[prev] ? i : prev), 0);

// Examples
indexOfMax([1, 3, 9, 7, 5]); // 2
indexOfMax([1, 3, 7, 7, 5]); // 2

const indexOfMin = (arr) => arr.reduce((prev, curr, i, a) => (curr < a[prev] ? i : prev), 0);

// Examples
indexOfMin([6, 4, 8, 2, 10]); // 3
indexOfMin([6, 4, 2, 2, 10]); // 2

const findLongest = (words) => Math.max(...words.map((el) => el.length));

// Example
findLongest(['always', 'look', 'on', 'the', 'bright', 'side', 'of', 'life']); // 6

const maxBy = (arr, key) => arr.reduce((a, b) => (a[key] >= b[key] ? a : b), {});

// Example
const people = [
    { name: 'Bar', age: 24 },
    { name: 'Baz', age: 32 },
    { name: 'Foo', age: 42 },
    { name: 'Fuzz', age: 36 },
];
maxBy(people, 'age'); // { name: 'Foo', age: 42 }

const max = (arr) => Math.max(...arr);

const minBy = (arr, key) => arr.reduce((a, b) => (a[key] < b[key] ? a : b), {});

// Example
const people = [
    { name: 'Bar', age: 24 },
    { name: 'Baz', age: 32 },
    { name: 'Foo', age: 42 },
    { name: 'Fuzz', age: 36 },
];
minBy(people, 'age'); // { name: 'Bar', age: 24 }

const min = (arr) => Math.min(...arr);

const flat = (arr) =>
    [].concat.apply(
        [],
        arr.map((a) => (Array.isArray(a) ? flat(a) : a))
    );
// Or
const flat = (arr) => arr.reduce((a, b) => (Array.isArray(b) ? [...a, ...flat(b)] : [...a, b]), []);

// Or
// See the browser compatibility at https://caniuse.com/#feat=array-flat
const flat = (arr) => arr.flat();

// Example
flat(['cat', ['lion', 'tiger']]); // ['cat', 'lion', 'tiger']

const getConsecutiveArrays = (arr, size) =>
    size > arr.length ? [] : arr.slice(size - 1).map((_, i) => arr.slice(i, size + i));

// Examples
getConsecutiveArrays([1, 2, 3, 4, 5], 2); // [[1, 2], [2, 3], [3, 4], [4, 5]]
getConsecutiveArrays([1, 2, 3, 4, 5], 3); // [[1, 2, 3], [2, 3, 4], [3, 4, 5]]
getConsecutiveArrays([1, 2, 3, 4, 5], 6); // []

const getNthItems = (arr, nth) => arr.filter((_, i) => i % nth === nth - 1);

// Examples
getNthItems([1, 2, 3, 4, 5, 6, 7, 8, 9], 2); // [2, 4, 6, 8]
getNthItems([1, 2, 3, 4, 5, 6, 7, 8, 9], 3); // [3, 6, 9]

const getSubsets = (arr) => arr.reduce((prev, curr) => prev.concat(prev.map((k) => k.concat(curr))), [[]]);

// Examples
getSubsets([1, 2]); // [[], [1], [2], [1, 2]]
getSubsets([1, 2, 3]); // [[], [1], [2], [1, 2], [3], [1, 3], [2, 3], [1, 2, 3]]

const indices = (arr, value) => arr.reduce((acc, v, i) => (v === value ? [...acc, i] : acc), []);

// Or
const indices = (arr, value) => arr.map((v, i) => (v === value ? i : false)).filter(Boolean);

// Examples
indices(['h', 'e', 'l', 'l', 'o'], 'l'); // [2, 3]
indices(['h', 'e', 'l', 'l', 'o'], 'w'); // []

const average = (arr) => arr.reduce((a, b) => a + b, 0) / arr.length;

const getIntersection = (a, ...arr) => [...new Set(a)].filter((v) => arr.every((b) => b.includes(v)));

// Examples
getIntersection([1, 2, 3], [2, 3, 4, 5]); // [2, 3]
getIntersection([1, 2, 3], [2, 3, 4, 5], [1, 3, 5]); // [3]

const ranking = (arr) => arr.map((x, y, z) => z.filter((w) => w > x).length + 1);

// Examples
ranking([80, 65, 90, 50]); // [2, 3, 1, 4]
ranking([80, 80, 70, 50]); // [1, 1, 3, 4]
ranking([80, 80, 80, 50]); // [1, 1, 1, 4]

const sum = (arr) => arr.reduce((a, b) => a + b, 0);

const unique = (arr) => [...new Set(arr)];

// Or
const unique = (arr) => arr.filter((el, i, array) => array.indexOf(el) === i);

// Or
const unique = (arr) => arr.reduce((acc, el) => (acc.includes(el) ? acc : [...acc, el]), []);

const union = (...arr) => [...new Set(arr.flat())];

// Example
union([1, 2], [2, 3], [3]); // [1, 2, 3]

const groupBy = (arr, key) =>
    arr.reduce((acc, item) => ((acc[item[key]] = [...(acc[item[key]] || []), item]), acc), {});

// Example
groupBy(
    [
        { branch: 'audi', model: 'q8', year: '2019' },
        { branch: 'audi', model: 'rs7', year: '2020' },
        { branch: 'ford', model: 'mustang', year: '2019' },
        { branch: 'ford', model: 'explorer', year: '2020' },
        { branch: 'bmw', model: 'x7', year: '2020' },
    ],
    'branch'
);

/*
{
    audi: [
        { branch: 'audi', model: 'q8', year: '2019' },
        { branch: 'audi', model: 'rs7', year: '2020' }
    ],
    bmw: [
        { branch: 'bmw', model: 'x7', year: '2020' }
    ],
    ford: [
        { branch: 'ford', model: 'mustang', year: '2019' },
        { branch: 'ford', model: 'explorer', year: '2020' }
    ],
}
*/

// Merge but don't remove the duplications
const merge = (a, b) => a.concat(b);
// Or
const merge = (a, b) => [...a, ...b];

// Merge and remove the duplications
const merge = [...new Set(a.concat(b))];
// Or
const merge = [...new Set([...a, ...b])];

const partition = (arr, criteria) => arr.reduce((acc, i) => (acc[criteria(i) ? 0 : 1].push(i), acc), [[], []]);

// Example
partition([1, 2, 3, 4, 5], (n) => n % 2); // [[1, 3, 5], [2, 4]]

const removeDuplicate = (arr) => arr.filter((i) => arr.indexOf(i) === arr.lastIndexOf(i));

// Example
removeDuplicate(['h', 'e', 'l', 'l', 'o', 'w', 'o', 'r', 'l', 'd']); //  ['h', 'e', 'w', 'r', 'd']

const removeFalsy = (arr) => arr.filter(Boolean);

// Example
removeFalsy([0, 'a string', '', NaN, true, 5, undefined, 'another string', false]); // ['a string', true, 5, 'another string']

// `arr` is an array
const repeat = (arr, n) => [].concat(...Array(n).fill(arr));

// Or
const repeat = (arr, n) => Array(n).fill(arr).flat();

// Or
const repeat = (arr, n) =>
    Array(arr.length * n)
        .fill(0)
        .map((_, i) => arr[i % arr.length]);

// Or
const repeat = (arr, n) => Array.from({ length: arr.length * n }, (_, i) => arr[i % arr.length]);

// Examples
repeat([1, 2, 3], 3); // [1, 2, 3, 1, 2, 3, 1, 2, 3]

const shuffle = (arr) =>
    arr
        .map((a) => ({ sort: Math.random(), value: a }))
        .sort((a, b) => a.sort - b.sort)
        .map((a) => a.value);

// Or
const shuffle = (arr) => arr.sort(() => 0.5 - Math.random());

// Example
shuffle([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]); // [9, 1, 10, 6, 8, 5, 2, 3, 7, 4]

const sortBy = (arr, k) => arr.concat().sort((a, b) => (a[k] > b[k] ? 1 : a[k] < b[k] ? -1 : 0));

// Example
const people = [
    { name: 'Foo', age: 42 },
    { name: 'Bar', age: 24 },
    { name: 'Fuzz', age: 36 },
    { name: 'Baz', age: 32 },
];
sortBy(people, 'age');

// returns
//  [
//      { name: 'Bar', age: 24 },
//      { name: 'Baz', age: 32 },
//      { name: 'Fuzz', age: 36 },
//      { name: 'Foo', age: 42 },
//  ]

const sort = (arr) => arr.sort((a, b) => a - b);

// Example
sort([1, 5, 2, 4, 3]); // [1, 2, 3, 4, 5]

const chunk = (arr, size) =>
    arr.reduce((acc, e, i) => (i % size ? acc[acc.length - 1].push(e) : acc.push([e]), acc), []);

// Examples
chunk([1, 2, 3, 4, 5, 6, 7, 8], 3); // [[1, 2, 3], [4, 5, 6], [7, 8]]
chunk([1, 2, 3, 4, 5, 6, 7, 8], 4); // [[1, 2, 3, 4], [5, 6, 7, 8]]

const transpose = (matrix) => matrix[0].map((col, i) => matrix.map((row) => row[i]));

// Or
const transpose = (matrix) => matrix[0].map((col, c) => matrix.map((row, r) => matrix[r][c]));

// Or
const transpose = (matrix) => matrix.reduce((prev, next) => next.map((item, i) => (prev[i] || []).concat(next[i])), []);

// Example
transpose([
    // [
    [1, 2, 3], //      [1, 4, 7],
    [4, 5, 6], //      [2, 5, 8],
    [7, 8, 9], //      [3, 6, 9],
]); //  ]

// `i` must be less than `j`
const swapItems = (a, i, j) =>
    (a[i] && a[j] && [...a.slice(0, i), a[j], ...a.slice(i + 1, j), a[i], ...a.slice(j + 1)]) || a;

// Example
swapItems([1, 2, 3, 4, 5], 1, 4); // [1, 5, 3, 4, 2]

const unzip = (arr) =>
    arr.reduce(
        (acc, c) => (c.forEach((v, i) => acc[i].push(v)), acc),
        Array.from({ length: Math.max(...arr.map((a) => a.length)) }, (_) => [])
    );

// Example
unzip([
    ['a', 1],
    ['b', 2],
    ['c', 3],
    ['d', 4],
    ['e', 5],
]); // [['a', 'b', 'c', 'd', 'e'], [1, 2, 3, 4, 5]]

/*
    a     1
     b   2
      c 3
      d 4
      e 5
*/

const zip = (...arr) => Array.from({ length: Math.max(...arr.map((a) => a.length)) }, (_, i) => arr.map((a) => a[i]));

// Example
zip(['a', 'b', 'c', 'd', 'e'], [1, 2, 3, 4, 5]); // [['a', 1], ['b', 2], ['c', 3], ['d', 4], ['e', 5]]

/*
Does it look like a zipper?
        a 1
        b 2
       c   3
      d     4
     e       5
*/

// `h` is an hour number between 0 and 23
const suffixAmPm = (h) => `${h % 12 === 0 ? 12 : h % 12}${h < 12 ? 'am' : 'pm'}`;

// Examples
suffixAmPm(0); // '12am'
suffixAmPm(5); // '5am'
suffixAmPm(12); // '12pm'
suffixAmPm(15); // '3pm'
suffixAmPm(23); // '11pm'

const diffDays = (date, otherDate) => Math.ceil(Math.abs(date - otherDate) / (1000 * 60 * 60 * 24));

// Example
diffDays(new Date('2014-12-19'), new Date('2020-01-01')); // 1839

const monthDiff = (startDate, endDate) =>
    Math.max(0, (endDate.getFullYear() - startDate.getFullYear()) * 12 - startDate.getMonth() + endDate.getMonth());

// Example
monthDiff(new Date('2020-01-01'), new Date('2021-01-01')); // 12

// `a` and `b` are `Date` instances
const compare = (a, b) => a.getTime() > b.getTime();

// Example
compare(new Date('2020-03-30'), new Date('2020-01-01')); // true

// `date` is a `Date` object
const formatYmd = (date) => date.toISOString().slice(0, 10);

// Example
formatYmd(new Date()); // 2020-05-06

// `s` is number of seconds
const formatSeconds = (s) => new Date(s * 1000).toISOString().substr(11, 8);

// Or
const formatSeconds = (s) => new Date(s * 1000).toUTCString().match(/(\d\d:\d\d:\d\d)/)[0];

// Or
const formatSeconds = (s) =>
    [parseInt(s / 60 / 60), parseInt((s / 60) % 60), parseInt(s % 60)].join(':').replace(/\b(\d)\b/g, '0$1');

// Examples
formatSeconds(200); // 00:03:20
formatSeconds(500); // 00:08:20

// `date` is a `Date` object
const extract = (date) =>
    date
        .toISOString()
        .split(/[^0-9]/)
        .slice(0, -1);

// `extract` is an array of [year, month, day, hour, minute, second, millisecond]

// `date` is a `Date` object
// `locale` is a locale (en-US, pt-BR, for example)
const format = (date, locale) => new Intl.DateTimeFormat(locale).format(date);

// Example
format(new Date(), 'pt-BR'); // 06/05/2020

const getQuarter = (d = new Date()) => Math.ceil((d.getMonth() + 1) / 3);

const ts = () => Math.floor(new Date().getTime() / 1000);

// `date` is a Date object
const dayOfYear = (date) => Math.floor((date - new Date(date.getFullYear(), 0, 0)) / (1000 * 60 * 60 * 24));

// Example
dayOfYear(new Date(2020, 04, 16)); // 137

const getFirstDate = (d = new Date()) => new Date(d.getFullYear(), d.getMonth(), 1);

const getLastDate = (d = new Date()) => new Date(d.getFullYear(), d.getMonth() + 1, 0);

// `date` is a Date object
const getMonthName = (date) =>
    [
        'January',
        'February',
        'March',
        'April',
        'May',
        'June',
        'July',
        'August',
        'September',
        'October',
        ' November',
        'December',
    ][date.getMonth()];

// `month` is zero-based index
const daysInMonth = (month, year) => new Date(year, month, 0).getDate();

const getTimezone = () => Intl.DateTimeFormat().resolvedOptions().timeZone;

// Example
getTimezone(); // 'Asia/Saigon'

const tomorrow = ((d) => new Date(d.setDate(d.getDate() + 1)))(new Date());

// Or
const tomorrow = new Date(new Date().valueOf() + 1000 * 60 * 60 * 24);

const numberOfDays = (year) => ((year % 4 === 0 && year % 100 !== 0) || year % 400 === 0 ? 366 : 365);

// Or
const numberOfDays = (year) => (new Date(year, 1, 29).getDate() === 29 ? 366 : 365);

// `date` is a Date object
const getWeekday = (date) =>
    ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'][date.getDay()];

const yesterday = ((d) => new Date(d.setDate(d.getDate() - 1)))(new Date());

// Or
const yesterday = new Date(new Date().valueOf() - 1000 * 60 * 60 * 24);