275 个最喜欢的JavaScript实用工具

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 }), {});

// 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); // [[2, 4], [1, 3, 5]]

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']

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
*/

const isDescendant = (child, parent) => parent.contains(child);

const hasFocus = (ele) => ele === document.activeElement;

const touchSupported = () =>
  "ontouchstart" in window ||
  (window.DocumentTouch && document instanceof window.DocumentTouch);

const isAtBottom = () =>
  document.documentElement.clientHeight + window.scrollY >=
  document.documentElement.scrollHeight;

const isIE = !!document.documentMode;

const isMacBrowser = /Mac|iPod|iPhone|iPad/.test(navigator.platform);

const siblings = (ele) =>
  [].slice.call(ele.parentNode.children).filter((child) => child !== ele);

const getPosition = (ele) => (
  (r = ele.getBoundingClientRect()),
  { left: r.left + window.scrollX, top: r.top + window.scrollY }
);

// Example
getPosition(document.body); // { left: 0, top: 0 }

const getSelectedText = () => window.getSelection().toString();

history.back();

// Or
history.go(-1);

// Pick the method that is suitable for your use case
const hide = (ele) => (ele.style.display = "none");

// Or
const hide = (ele) => (ele.style.visibility = "hidden");

// Or
const hide = (ele) => (ele.hidden = true);

const insertAfter = (ele, anotherEle) =>
  anotherEle.parentNode.insertBefore(ele, anotherEle.nextSibling);

// Or
const insertAfter = (ele, anotherEle) =>
  anotherEle.insertAdjacentElement("afterend", ele);

const insertBefore = (ele, anotherEle) =>
  anotherEle.parentNode.insertBefore(ele, anotherEle);

// Or
const insertBefore = (ele, anotherEle) =>
  anotherEle.insertAdjacentElement("beforebegin", ele);

const insertHtmlAfter = (html, ele) => ele.insertAdjacentHTML("afterend", html);

const insertHtmlBefore = (html, ele) =>
  ele.insertAdjacentHTML("beforebegin", html);

const goTo = (url) => (location.href = url);

const reload = () => location.reload();

// Or
const reload = () => (location.href = location.href);

const replace = (ele, newEle) => ele.parentNode.replaceChild(newEle, ele);

const goToTop = () => window.scrollTo(0, 0);

const serialize = (formEle) =>
  Array.from(new FormData(formEle)).reduce(
    (p, [k, v]) =>
      Object.assign({}, p, {
        [k]: p[k] ? (Array.isArray(p[k]) ? p[k] : [p[k]]).concat(v) : v,
      }),
    {}
  );

const show = (ele) => (ele.style.display = "");

const stripHtml = (html) =>
  new DOMParser().parseFromString(html, "text/html").body.textContent || "";

const toggle = (ele) =>
  (ele.style.display = ele.style.display === "none" ? "block" : "none");

// Or
const toggle = (ele) => (ele.hidden = !ele.hidden);

// `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);

const midnightOfToday = () => new Date(new Date().setHours(0, 0, 0, 0));

// `arr` is an array of `Date` items
const sortDescending = (arr) => arr.sort((a, b) => a.getTime() > b.getTime());
const sortAscending = (arr) => arr.sort((a, b) => a.getTime() < b.getTime());

const boxHandler = x => ({ next: f => boxHandler(f(x)), done: f => f(x) });

// Example 1
const getPercentNumber = str => boxHandler(str).next(str => str.replace(/\%/, '')).next(str => parseFloat(str)).done(res => res * 0.01);

getPercentNumber('50%');    // 0.5

// Example 2
const getMoney = (price) => Number.parseFloat(price.replace(/\$/, ''));
const getPercent = (percent) => Number.parseFloat(percent.replace(/\%/)) * 0.01;

const getDiscountPrice = (price, discount) => boxHandler(getMoney(price)).done(cents => boxHandler(getPercent(discount)).next(save => cents - (cents * save))).done(res => res);

getDiscountPrice('$6.00', '20%');    // 4.8

const isFunction = (v) =>
  [
    "[object Function]",
    "[object GeneratorFunction]",
    "[object AsyncFunction]",
    "[object Promise]",
  ].includes(Object.prototype.toString.call(v));

// Examples
isFunction(function () {}); // true
isFunction(function* () {}); // true
isFunction(async function () {}); // true

const isGeneratorFunction = (v) =>
  Object.prototype.toString.call(v) === "[object GeneratorFunction]";

// Examples
isGeneratorFunction(function () {}); // false
isGeneratorFunction(function* () {}); // true

const isAsyncFunction = (v) =>
  Object.prototype.toString.call(v) === "[object AsyncFunction]";

// Examples
isAsyncFunction(function () {}); // false
isAsyncFunction(function* () {}); // false
isAsyncFunction(async function () {}); // true

// Compose functions from left to right
const pipe =
  (...fns) =>
  (x) =>
    fns.reduce((y, f) => f(y), x);

// Example
const lowercase = (str) => str.toLowerCase();
const capitalize = (str) => `${str.charAt(0).toUpperCase()}${str.slice(1)}`;
const reverse = (str) => str.split("").reverse().join("");

const fn = pipe(lowercase, capitalize, reverse);

// We will execute `lowercase`, `capitalize` and `reverse` in order
fn("Hello World") === "dlrow olleH";

// Compose functions from right to left
const compose =
  (...fns) =>
  (x) =>
    fns.reduceRight((y, f) => f(y), x);

// Example
const lowercase = (str) => str.toLowerCase();
const capitalize = (str) => `${str.charAt(0).toUpperCase()}${str.slice(1)}`;
const reverse = (str) => str.split("").reverse().join("");

const fn = compose(reverse, capitalize, lowercase);

// We will execute `lowercase`, `capitalize` and `reverse` in order
fn("Hello World") === "dlrow olleH";

const unary = (fn) => (arg) => fn(arg);

// Example
["1", "2", "3", "4", "5"].map(unary(parseInt)); // [1, 2, 3, 4, 5]

const noop = () => {};

// Or
const noop = Function();
// calling Function() might be detected as using eval by some security tools

const curry = (fn, ...args) =>
  fn.length <= args.length ? fn(...args) : curry.bind(null, fn, ...args);

// Example
const sum = (a, b, c) => a + b + c;
curry(sum)(1)(2)(3); // 6
curry(sum)(1, 2, 3); // 6
curry(sum, 1)(2, 3); // 6
curry(sum, 1)(2)(3); // 6
curry(sum, 1, 2)(3); // 6
curry(sum, 1, 2, 3); // 6

// returns a new version of `fn` that returns values as lazy evaluable
const thunkfy =
  (fn) =>
  (...args) =>
  () =>
    fn(...args);

// Example
const heavyComputation = (x) => doStuff(x);
const unnecessarySlow = manyThings
  .map(heavyComputation)
  .find((result) => result.criteria);
const probablyFaster = manyThings
  .map(thunkfy(heavyComputation))
  .find((thunk) => thunk().criteria);

const once = (fn) =>
  (
    (ran = false) =>
    () =>
      ran ? fn : ((ran = !ran), (fn = fn()))
  )();

// Example
let n = 0;
const incOnce = once(() => ++n);
incOnce(); // n = 1
incOnce(); // n = 1
incOnce(); // n = 1

// Reverse the order of arguments
const flip =
  (fn) =>
  (...args) =>
    fn(...args.reverse());

// For binary functions
const flip = (fn) => (b, a) => fn(a, b);

// Or for curried functions
const flip = (fn) => (b) => (a) => fn(a)(b);

// Example
const isParent = (parent, child) => parent.children.includes(child);
const isChild = flip(isParent);

const identity = (x) => x;

// returns `true` if one of the arguments is truthy and the other is falsy

const xor = (a, b) => (a && !b) || (!a && b);

// Or
const xor = (a, b) => !(!a && !b) && !(a && b);

// Or
const xor = (a, b) => Boolean(!a ^ !b);

// Examples
xor(true, true); // false
xor(false, false); // false
xor(true, false); // true
xor(false, true); // true

const memoize = (fn) =>
  (
    (cache = {}) =>
    (arg) =>
      cache[arg] || (cache[arg] = fn(arg))
  )();

// Example
// Calculate Fibonacci numbers
const fibo = memoize((n) => (n <= 2 ? 1 : fibo(n - 1) + fibo(n - 2)));

fibo(1); // 1
fibo(2); // 1
fibo(3); // 2
fibo(4); // 3
fibo(5); // 5
fibo(6); // 8

const partial =
  (fn, ...a) =>
  (...b) =>
    fn(...a, ...b);

// Example
const sum = (x, y) => x + y;
const inc = partial(sum, 1);
inc(9); // 10

// `fn` is a curried function
// `n` is the depth of parameters
const uncurry =
  (fn, n = 1) =>
  (...args) =>
    (
      (acc) => (args) =>
        args.reduce((x, y) => x(y), acc)
    )(fn)(args.slice(0, n));

// Example
const sum = (a) => (b) => (c) => a + b + c;
uncurry(sum, 1)(1)(2)(3); // 6
uncurry(sum, 2)(1, 2)(3); // 6
uncurry(sum, 3)(1, 2, 3); // 6

// In radians
const radiansAngle = (p1, p2) => Math.atan2(p2.y - p1.y, p2.x - p1.x);

// In degrees
const degreesAngle = (p1, p2) =>
  (Math.atan2(p2.y - p1.y, p2.x - p1.x) * 180) / Math.PI;

const distance = (p1, p2) =>
  Math.sqrt(Math.pow(p2.x - p1.x, 2) + Math.pow(p2.y - p1.y, 2));

const midpoint = (p1, p2) => [(p1.x + p2.x) / 2, (p1.y + p2.y) / 2];

const isInside = (point, rect) =>
  point.x > rect.left &&
  point.x < rect.right &&
  point.y > rect.top &&
  point.y < rect.bottom;

// Returns true if `a` contains `b`
// (x1, y1) and (x2, y2) are top-left and bottom-right corners
const contains = (a, b) =>
  a.x1 <= b.x1 && a.y1 <= b.y1 && a.x2 >= b.x2 && a.y2 >= b.y2;

// Returns true if `a` overlaps `b`
// (x1, y1) and (x2, y2) are top-left and bottom-right corners
const overlaps = (a, b) =>
  (a.x1 < b.x2 && b.x1 < a.x2) || (a.y1 < b.y2 && b.y1 < a.y2);

const degsToRads = (deg) => (deg * Math.PI) / 180.0;