std

Installation

1npm install @sandstreamdev/std

Documentation

array

any

Checks if the given array is present and it is not empty (contains at least one element).

Type signature

1<T>(xs?: T[]) => boolean

Examples

1any([]);
2// ⇒ false

1any([1, 2, 3]);
2// ⇒ true

Questions

• How to check if an array is empty?
• How to check if an array is empty or null or undefined?
• How to check if an array is empty or not?
• How to check if an array is empty or doesn't exist?

are

Checks if the given arguments are all Arrays.

Type signature

1<T>(...xs: T[]) => boolean

Examples

1are([2, 3]);
2// ⇒ true

1are([1, 2, 3], []);
2// ⇒ true

1are([1, 2, 3], 8, [1, 3], "test");
2// ⇒ false

Questions

• How to check if all the given values are arrays?

chunk

Splits the given array into an array of chunks of up to the given length.

Type signature

1(count: number) => <T>(xs: T[]) => T[] | T[][]

Examples

1chunk(2)(['a', 'b', 'c', 'd']);
2// ⇒ [['a', 'b'], ['c', 'd']]

1chunk(3)(['a', 'b', 'c', 'd']);
2// ⇒ [['a', 'b', 'c'], ['d']]

Questions

• How to split an array into chunks?
• How to split an array into chunks of the same size?

difference

Computes a set difference between the two given arrays.

Type signature

1<T>(xs: T[], ys: T[]) => T[]

Examples

1difference([1, 2, 3, 4, 5, 6], [2, 4]);
2// ⇒ [1, 3, 5, 6]

Questions

• How to find elements which are present in the first array and not in the second?

differs

Checks if two arrays are not equal.

Type signature

1<T>(xs?: T[], ys?: T[]) => boolean

Examples

1differs([1, 2, 3], [1, 2]);
2// ⇒ true

1differs([1, 2, 3], [1, 2, 3]);
2// ⇒ false

Questions

• How to check if two arrays differ?
• How to check if two arrays are not equal?
• How to check if two arrays are equal or not?

duplicates

Lists all the duplicated values in the given array.

Type signature

1<T>(xs: T[]) => T[]

Examples

1duplicates([1, 2, 3, 4, 3, 4, 3, 6]);
2// ⇒ [3, 4, 3]

Questions

• How to find duplicates in an array?

empty

Empty array.

Type signature

1unknown[]

Examples

1empty;
2// ⇒ []

Questions

• How to get an empty array?

exact

Takes exactly the given count of elements.

Type signature

1(count: number) => <T>(xs: T[]) => T[]

Examples

1exact(5)([1, 2, 3]);
2// ⇒ [1, 2, 3, undefined, undefined]

1exact(2)([1, 2, 3]);
2// ⇒ [1, 2]

Questions

• How to get exactly N elements out of an array?

except

Filters out the given value.

Type signature

1<T>(y: T) => (xs: T[]) => T[]

Examples

1except(2)([1, 2, 3, 4, 5]);
2// ⇒ [1, 3, 4, 5]

1except(2)([1, 2, 2, 4, 2]);
2// ⇒ [1, 4]

Questions

• How to get all the values of an array except the given one?

filterInPlace

Filters the given array with the given predicate just like Array.filter but does it in-place thus mutates the original array.

Type signature

1<T>(f: (value: T, index: number, context: T[]) => boolean) => (xs: T[]) => T[]

Examples

1const xs = [1, 2, 3, 4, 5, 6, 7];
2const odd = x => x % 2 === 1;
3
4const ys = filterInPlace(odd)(xs);
5
6ys === xs;
7// ⇒ true
8ys;
9// ⇒ [1, 3, 5, 7]

Questions

• How to filter an array in place?

find

Finds an element by a predicate function within the given array, otherwise, it returns the given fallback value or undefined when fallback is not present.

Type signature

1<T>(predicate: (value: T, index: number, context: T[]) => boolean, fallback?: T) => (xs: T[]) => T

Examples

1find(x => x > 2)([1, 2, 3, 5, 7]);
2// ⇒ 3

1find(x => x > 2)([1, 2, -3, -5, -7]);
2// ⇒ undefined

Questions

• How to find an element of an array by a given predicate?

first

Returns the first element or undefined when there are no elements in the given array.

Type signature

1<T>([x]: T[]) => T | undefined

Examples

1first([1, 2, 3]);
2// ⇒ 1

1first([]);
2// ⇒ undefined

Questions

• How to get the first element of an array?

flatMap

Maps and flattens the result.

Type signature

1<T, TResult>(f: (value: T, index: number, context: T[]) => TResult[]) => (xs: T[]) => TResult[]

Examples

1flatMap(text => [...text])(["test", "123"]);
2// ⇒ ["t", "e", "s", "t", "1", "2", "3"]

Questions

• How to flat map an array?
• How to map and then flatten an array?

flatten

Flattens the nested arrays by a single level.

Type signature

1<T>(xs: T[]) => T[]

Examples

1flatten([1, [2, 3], 4, [5, 6]]);
2// ⇒ [1, 2, 3, 4, 5, 6]

1flatten([1, [2, [3, 6]], 4, [5, 6]]);
2// ⇒ [1, 2, [3, 6], 4, 5, 6]

Questions

• How to flatten an array?

insert

Inserts the given item to the array at a specific index.

Type signature

1(index: number) => <T>(item: T) => ([...xs]: T[]) => T[]

Examples

1insert(0)('d')(['a', 'b', 'c']);
2// ⇒ ['d', 'a', 'b', 'c']

1insert(1)('d')(['a', 'b', 'c']);
2// ⇒ ['a', 'd', 'b', 'c']

Questions

• How to insert an element to an array at a given position?

intersection

Finds common elements between both arrays.

Type signature

1<T>(xs: T[], ys: T[]) => T[]

Examples

1intersection([1, 2, 3, 4, 5], [5, 5, 3, 2]);
2// ⇒ [2, 3, 5]

Questions

• How to find common elements present in both arrays?

is

Checks if the given argument is an array.

Type signature

1(value?: unknown) => boolean

Examples

1is([1, 2, 3]);
2// ⇒ true

1is({ a: 5 });
2// ⇒ false

Questions

• How to check if a value is an array?

last

Returns the last element or undefined when there are no elements in the given array.

Type signature

1<T>(xs: T[]) => T | undefined

Examples

1last([1, 2, 3]);
2// ⇒ 3

1last([]);
2// ⇒ undefined

Questions

• How to get the last element of an array?

length

Returns the number of elements in the given array.

Type signature

1<T>(xs: T[]) => number

Examples

1length([true, 1]);
2// ⇒ 2

1length([1, 2, 3]);
2// ⇒ 3

1length([]);
2// ⇒ 0

Questions

• How to check an array's length?
• How to compute an array's length?
• How to check the size of an array?
• How to check the number of elements in an array?

lengthDiffers

Checks if lengths of the given arrays differ.

Type signature

1<T1, T2>(a: T1[], b: T2[]) => boolean

Examples

1lengthDiffers([1, 2, 3], [1, 2]);
2// ⇒ true

1lengthDiffers([6, 7], [1, 2]);
2// ⇒ false

Questions

• How to check if array lengths differ?
• How to check if the given arrays have different lengths?

map

Maps the given array with the given functions.

Type signature

1<T>(...fs: ((x: T) => T)[]) => (xs: T[]) => T[]

Examples

1map(x => x * x)([1, 2, 3]);
2// ⇒ [1, 4, 9]

1map(x => x * x, x => x + 1)([1, 2, 3]);
2// ⇒ [2, 5, 10]

Questions

• How to map an array?

midpoint

Returns the middle element or the right one when the number of elements is even.

Type signature

1<T>(xs: T[]) => T | undefined

Examples

1midpoint([1, 2, 3, 4, 5]);
2// ⇒ 3

1midpoint([1, 2, 3, 4]);
2// ⇒ 3

Questions

• How to get the element in the middle of an array?
• How to get the middle element of an array?

minMax

Computes minimum and maximum values of the given array in a single run.

Type signature

1(xs: number[]) => number[]

Examples

1minMax([10, 5, 3, -5, -4, 23, 32, 8, 1, 0]);
2// ⇒ [-5, 32]

1minMax([1]);
2// ⇒ [1, 1]

1minMax([]);
2// ⇒ [undefined, undefined]

Questions

• How to find the minimum and maximum values of an array?
• How to get the min/max element of an array?

multiple

Checks if the given array contains more than one element.

Type signature

1<T>(xs: T[]) => boolean

Examples

1multiple([1, 2, 3]);
2// ⇒ true

1multiple([1, 2]);
2// ⇒ true

1multiple([1]);
2// ⇒ false

1multiple([]);
2// ⇒ false

Questions

• How to check if an array contains multiple elements?
• How to check whether multiple values exist within an array?

none

Checks if the given array is empty.

Type signature

1<T>(xs?: T[]) => boolean

Examples

1none([]);
2// ⇒ true

1none([1, 2, 3]);
2// ⇒ false

Questions

• How to check if an array is empty?

partition

Partitions the given array to the ones that pass the given predicate function and the ones that do not. By convention of the Haskell's Data.Either, values that pass the predicate are placed at the right.

Type signature

1<T>(predicate: (x: T) => boolean) => (xs: T[]) => readonly [T[], T[]]

Examples

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

Questions

• How to partition an array based on a condition?
• How to divide an array by a filter function?

pop

Returns the given array without the last element.

Type signature

1<T>(xs: T[]) => T[]

Examples

1pop([1, 2, 3, 4]); // ⇒ [1, 2, 3]

1pop([]); // ⇒ []

Questions

• How to get an array without the last element?
• How to remove the last element from an array?

range

Generates an array of numbers from 0 to n - 1.

Type signature

1(n: number) => number[]

Examples

1range(3);
2// ⇒ [0, 1, 2]

Questions

• How to create an array of all integers from 0 to N exclusive?

removeAt

Removes an element at the given index from the given array.

Type signature

1(index: number) => <T>(xs: T[]) => T[]

Examples

1removeAt(3)([1, 2, 3, 4, 5, 6])
2// ⇒ [1, 2, 3, 5, 6]

Questions

• How to remove an item from an array at a particular index?

repeat

Repeats the given element by the given count of times.

Type signature

1(count: number) => <T>(value: T) => T[]

Examples

1repeat(3)("test");
2// ⇒ ["test", "test", "test"]

Questions

• How to repeat a value N times?

reverse

Reverses the given array without mutating it (in contrast to Array.reverse).

Type signature

1<T>(xs: T[]) => T[]

Examples

1reverse([1, 2, 3, 4, 5]);
2// ⇒ [5, 4, 3, 2, 1]

Questions

• How to reverse an array without mutating it?

reverseIf

Reverses the given array when enabled.

Type signature

1(enabled: boolean) => <T>(xs: T[]) => T[]

Examples

1reverseIf(true)([1, 2, 3, 4, 5]);
2// ⇒ [5, 4, 3, 2, 1]

1reverseIf(false)([1, 2, 3, 4, 5]);
2// ⇒ [1, 2, 3, 4, 5]

Questions

• How to reverse an array without mutating it only when a condition is satisfied?

second

Returns the second element or undefined when there are less than two elements in the given array.

Type signature

1<T>(xs: T[]) => T | undefined

Examples

1second([1, 2, 3, 4, 5]);
2// ⇒ 2

1second([1]);
2// ⇒ undefined

1second([]);
2// ⇒ undefined

Questions

• How to get the second element of an array?

secondToLast

Returns the second to last element or undefined when there are less than two elements in the given array.

Type signature

1<T>(xs: T[]) => T | undefined

Examples

1secondToLast([1, 2, 3, 4, 5]);
2// ⇒ 4

1secondToLast([1]);
2// ⇒ undefined

1secondToLast([]);
2// ⇒ undefined

Questions

• How to get the second to last element of an array?

shift

Shifts the given array to the left and circulates the elements back by modulo of the array's length.

Type signature

1(count: number) => <T>(xs: T[]) => T[]

Examples

1shift(1)([1, 2, 3, 4, 5]);
2// ⇒ [2, 3, 4, 5, 1]

1shift(2)([1, 2, 3, 4, 5]);
2// ⇒ [3, 4, 5, 1, 2]

1shift(3)([1, 2, 3, 4, 5]);
2// ⇒ [4, 5, 1, 2, 3]

Questions

• How to shift an array?

shuffle

Shuffles the given array in random order with Math.random as the default.

Type signature

1<T>(xs: T[], random?: () => number) => T[]

Examples

1let i = 0;
2
3const random = () =>
4  [
5    0.013606630487694282,
6    0.21052486239086554,
7    0.28299838254636556,
8    0.696161009199874,
9    0.32165320593537117
10  ][i++];
11
12shuffle([1, 2, 3, 4, 5], random); // => [3, 5, 4, 2, 1]

Questions

• How to shuffle an array?

shuffleInPlace

Shuffles the given array in-place in random order with Math.random as the default.

Type signature

1<T>(xs: T[], random?: () => number) => T[]

Examples

1let i = 0;
2
3const random = () =>
4  [
5    0.013606630487694282,
6    0.21052486239086554,
7    0.28299838254636556,
8    0.696161009199874,
9    0.32165320593537117
10  ][i++];
11
12shuffleInPlace([1, 2, 3, 4, 5], random); // => [3, 5, 4, 2, 1]

Questions

• How to shuffle an array in place?

single

Checks if the given array contains exactly one element.

Type signature

1<T>(xs: T[]) => boolean

Examples

1single([1]);
2// ⇒ true

1single([1, 2, 3]);
2// ⇒ false

1single([]);
2// ⇒ false

Questions

• How to check if an array contains only one element?

skip

Skips the given count of elements from the given array.

Type signature

1(count: number) => <T>(xs: T[]) => T[]

Examples

1skip(2)([1, 2, 3, 4, 5]);
2// ⇒ [3, 4, 5]

Questions

• How to skip the first few elements of an array?

slidingWindow

Returns a new array composed of tuples of the given sliding window length of consecutive elements.

Type signature

1(count: number) => <T>(xs: T[]) => T[][]

Examples

1slidingWindow(2)([1, 2, 3, 4]);
2// ⇒ [[1, 2], [2, 3], [3, 4]]

1slidingWindow(3)([1, 2, 3, 4, 5]);
2// ⇒ [[1, 2, 3], [2, 3, 4], [3, 4, 5]]

1slidingWindow(1)([1, 2, 3, 4, 5, 6]);
2// ⇒ [[1], [2], [3], [4], [5], [6]]

Questions

• How to iterate an array pairwise?

sort

Sorts the given array without mutating it.

Type signature

1<T>(f?: (a: T, b: T) => number) => (xs: T[]) => T[]

Examples

1sort((a, b) => a - b)([13, 79, 20, 69, 44, 67, 18, 95, 26, 55]);
2// ⇒ [13, 18, 20, 26, 44, 55, 67, 69, 79, 95]

Questions

• How to sort an array without mutating it?

sum

Sums the given array of numbers.

Type signature

1(xs: number[]) => number

Examples

1sum([1, 2, 3, 4, 5]);
2// ⇒ 15

Questions

• How to sum elements of an array?

take

Takes up to a given count of elements.

Type signature

1(count: number) => <T>(xs: T[]) => T[]

Examples

1take(2)([1, 2, 3, 4, 5]);
2// ⇒ [1, 2]

1take(10)([1, 2, 3, 4, 5]);
2// ⇒ [1, 2, 3, 4, 5]

Questions

• How to get the first N number of elements from an array?

unique

Returns unique elements of the given array.

Type signature

1<T>(xs: T[]) => T[]

Examples

1unique([1, 2, 3, 4, 3, 4, 3, 6]);
2// ⇒ [1, 2, 3, 4, 6]

Questions

• How to find all unique values in an array?

uniqueBy

Filters out duplicated values based on the result of the given key selector.

Type signature

1<T, TResult>(f: (x: T) => TResult) => (xs: T[]) => T[]

Examples

1uniqueBy(({ id }) => id)([
2  { id: 1, value: 'a' },
3  { id: 2, value: 'b' },
4  { id: 1, value: 'c' }
5])
6// ⇒ [{ id: 1, value: 'c' }, { id: 2, value: 'b' }]

Questions

• How to find all unique values in an array by some predicate?

zip

Zips the given arrays together into pairs.

Type signature

1(xs: unknown[], ys: unknown[]) => [unknown, unknown][]

Examples

1zip([1, 2, 3], [4, 5, 6]);
2// ⇒ [[1, 4],[2, 5],[3, 6]]

Questions

• How to zip two arrays?

zipN

Zips the given arrays together into pairs.

Type signature

1<T>(...xs: T[][]) => T[][]

Examples

1zipN([1, 2, 3], [4, 5, 6]);
2// ⇒ [[1, 4], [2, 5], [3, 6]]

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

1zipN([1, 2], [4, 5, 6], [7, 8, 9]);
2// ⇒ [[1, 4, 7],[2, 5, 8]]

Questions

• How to zip multiple arrays?

zipWith

Zips the given arrays together with the given function.

Type signature

1<T1, T2>(f?: (x: T1, y: T2) => [T1, T2]) => (xs: T1[], ys: T2[]) => [T1, T2][]

Examples

1zipWith((x, y) => x * x + y)([1, 2, 3], [4, 5, 6]);
2// ⇒ [5, 9, 15]

Questions

• How to zip two arrays with a given function?

async

debounce

Makes the function run after the given period of not being called. Useful to delay input submission for auto-complete etc.

Type signature

1(f: F, wait: number) => (...args: unknown[]) => void

Examples

1const f = () => console.log("Test");
2
3const debounced = debounce(f, 2000);
4
5debounced();
6setTimeout(debounced, 1000);
7setTimeout(debounced, 3000);

Questions

• How to make function fire after some time not being called?
• How to debounce input events?
• How to debounce a function?

delay

When awaited, delays the execution by the given number of milliseconds.

Type signature

1(duration: number) => Promise<unknown>

Examples

1delay(2000)(() => console.log("Test"));

Questions

• How to delay a function?
• What is the JavaScript version of sleep()?

sequence

Runs the given tasks in a sequence.

Type signature

1<T>(tasks: Task<T>[]) => Promise<Awaited<T>[]>

Examples

1const f = () => new Promise(resolve => setTimeout(resolve, 1000));
2const g = () => new Promise(resolve => setTimeout(resolve, 2000));
3
4sequence([f, g]).then(() => console.log("Done"));

Questions

• How to run async tasks sequentially?

date

clamp

Clamps the given date to the given date range.

Type signature

1(min: Date, max: Date) => (date: Date) => Date

Examples

1const date = new Date("2019-06-15T13:54:33.232Z");
2const min = new Date("2019-02-23T13:54:33.232Z");
3const max = new Date("2019-03-13T13:54:33.232Z");
4
5clamp(min, max)(date);
6// => new Date("2019-03-13T13:54:33.232Z")

Questions

• How to clamp a date to the desired date range?
• How to enforce a date to be in a given date range?

clone

Clones the given Date object.

Type signature

1(date: Date) => Date

Examples

1const date = new new Date("2019-04-24T13:54:33.232Z");
2const cloned = clone(date);
3
4cloned !== date && cloned.valueOf() === date.valueOf();
5// ⇒ true

Questions

• How to clone a Date object?

dateDiff

Computes a signed difference between two Date objects as milliseconds.

Type signature

1(a: Date, b: Date) => number

Examples

1dateDiff(new Date("2017-01-01T13:00:00.000Z"), new Date("2017-01-01T12:00:00.000Z"));
2// ⇒ 3600000

Questions

• How to compute Date difference?

dateInRange

Checks if the given date is between the given date range (inclusive).

Type signature

1(from: Date, to: Date) => (date: Date) => boolean

Examples

1dateInRange(new Date("2018-06-10T12:00:00.000Z"), new Date("2018-06-20T12:00:00.000Z"))(new Date("2018-06-15T12:00:00.000Z"));
2// ⇒ true

Questions

• How to check if a date is within a given date range?

dayRange

Returns a local day range at a particular Date.

Type signature

1(date: Date) => Date[]

Examples

1const date = new Date("2018-12-31T13:54:33.232Z");
2
3dayRange(date);
4// ⇒ [startOfDay(date), endOfDay(date)]

Questions

• How to find a date range of a given day?

daysInMonths

Returns an array of days in a particular months. Number of days in February varies if it is a leap year or not.

Type signature

1(leapYear: boolean) => [number, number, number, number, number, number, number, number, number, number, number, number]

Examples

1daysInMonths(false);
2// ⇒ [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]

1daysInMonths(true);
2// ⇒ [31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]

Questions

• How to find out how many days are in a particular month?
• How to find out how many days there are in a leap year?

daysInYear

Calculates the number of days in a particular year. Varies by the leap year.

Type signature

1(year: number) => 366 | 365

Examples

1daysInYear(2019);
2// ⇒ 365

1daysInYear(2020);
2// ⇒ 366

Questions

• How many days are in a particular year?
• How many days are in a leap year?
• How many days are in a common year?

displayTime

Displays padded time string.

Type signature

1(source: [number, number, number], showSeconds: boolean) => string

Examples

1displayTime([5, 12, 16], false);
2// ⇒ 05:12

1displayTime([5, 12, 16], true);
2// ⇒ 05:12:16

Questions

• How to display padded time?

endOfDay

Returns a local Date of an end of the day at a particular Date.

Type signature

1(date: Date) => Date

Examples

1endOfDay(new Date("2018-12-31T13:54:33.232Z"));
2// ⇒ new Date(new Date("2019-01-01T00:00:00.000Z").valueOf() + new Date("2018-12-31T13:54:33.232Z").getTimezoneOffset() * 60 * 1000)

Questions

• How to find a date of an end of a given day?

formatDate

Formats a given date as a simple YYYY-MM-DD string.

Type signature

1(date: Date) => string

Examples

1formatDate(new Date("2019-02-24T01:12:34"));
2// ⇒ "2019-02-24"

Questions

• How to render a date in a YYYY-MM-DD format?

formatDateTime

Formats a given date as a simple YYYY-MM-DD HH:MM(:SS) string.

Type signature

1(sourceDate: Date, showSeconds?: boolean) => string

Examples

1formatDateTime(new Date("2019-02-24T01:12:34"));
2// ⇒ "2019-02-24 01:12"

1formatDateTime(new Date("2019-02-24T01:12:34"), true);
2// ⇒ "2019-02-24 01:12:34"

Questions

• How to render a date in a YYYY-MM-DD HH:MM format?
• How to render a date in a YYYY-MM-DD HH:MM:SS format?

formatDuration

Formats a duration in milliseconds to a padded time string.

Type signature

1(duration: number, showSeconds?: boolean) => string

Examples

1formatDuration(26100000);
2// ⇒ 07:15

1formatDuration(26136000, true);
2// ⇒ 07:15:36

Questions

• How to render a formatted duration?

formatTime

Formats a given date as a simple HH:MM(:SS) string.

Type signature

1(date: Date, showSeconds?: boolean) => string

Examples

1formatTime(new Date("2019-02-24T01:12:34"));
2// ⇒ "01:12"

1formatTime(new Date("2019-02-24T01:12:34"), true);
2// ⇒ "01:12:34"

Questions

• How to render a date in a HH:MM format?
• How to render a date in a HH:MM:SS format?

fromDays

Converts the given day count to milliseconds.

Type signature

1(days: number) => number

Examples

1fromDays(1);
2// ⇒ 86400000

Questions

• How to find how many milliseconds are in a given number of days?

fromHours

Converts the given hour count to milliseconds.

Type signature

1(hours: number) => number

Examples

1fromHours(1);
2// ⇒ 3600000

Questions

• How to find how many milliseconds are in a given number of hours?

fromMinutes

Converts the given minute count to milliseconds.

Type signature

1(minutes: number) => number

Examples

1fromMinutes(1);
2// ⇒ 60000

Questions

• How to find how many milliseconds are in a given number of minutes?

fromSeconds

Converts the given second count to milliseconds.

Type signature

1(seconds: number) => number

Examples

1fromSeconds(1);
2// ⇒ 1000

Questions

• How to find how many milliseconds are in a given number of seconds?

joinDateTime

Joins a date-time pair into a date-time string.

Type signature

1(date: string, time: string) => string

Examples

1joinDateTime("2019-01-15", "13:54:33.232Z");
2// ⇒ "2019-01-15T13:54:33.232Z"

Questions

• How to join date and time to get ISO-compliant date-time string?

leapYear

Detects if a given year is a leap year.

Type signature

1(year: number) => boolean

Examples

1leapYear(2020);
2// ⇒ true

1leapYear(2019);
2// ⇒ false

Questions

• How to find if the given year is a leap year?

parseHourMinutePair

Parses HH:MM string into hours and minutes.

Type signature

1(text?: string) => [number, number]

Examples

1parseHourMinutePair("12:34");
2// ⇒ [12, 34]

Questions

• How to parse time string into hours and minutes?

splitDateTime

Splits a date-time string into a date-time pair.

Type signature

1(dateTimeString: string) => [string, string]

Examples

1splitDateTime("2019-01-15T13:54:33.232Z");
2// ⇒ ["2019-01-15", "13:54:33.232Z"]

Questions

• How to split ISO-compliant date-time string into a date and time pair?

startOfDay

Returns a local Date of a start of the day at a particular Date.

Type signature

1(date: Date) => Date

Examples

1endOfDay(new Date("2019-01-01T13:54:33.232Z"));
2// ⇒ new Date(new Date("2019-01-01T00:00:00.000Z").valueOf() + new Date("2019-01-01T13:54:33.232Z").getTimezoneOffset() * 60 * 1000)

Questions

• How to find a date of the start of a given day?

subtractDays

Subtracts the given number of days from the given Date object.

Type signature

1(sourceDate: Date, numberOfDays: number) => Date

Examples

1subtractDays(new Date("2019-01-15T13:54:33.232Z"), 1);
2// ⇒ new Date("2019-01-14T13:54:33.232Z")

Questions

• How to subtract days from a given date?

toDate

Extracts padded YYYY-MM-DD date string out of the given date object.

Type signature

1(date: Date) => string

Examples

1toDate(new Date("2019-01-15T12:00:00.000Z"));
2// ⇒ "2019-01-15"

Questions

• How to get only the date from a Date object?

toDates

Converts the given array of values into Dates using the Date constructor.

Type signature

1(xs: (string | number | Date)[]) => Date[]

Examples

1toDates(["2019-01-15T13:54:33.232Z", new Date("2019-01-15T13:54:33.232Z").valueOf(), new Date("2019-01-15T13:54:33.232Z")]);
2// ⇒ [new Date("2019-01-15T13:54:33.232Z"), new Date("2019-01-15T13:54:33.232Z"), new Date("2019-01-15T13:54:33.232Z")]

Questions

• How to convert an array of string and timestamps into an array of Date objects?

toDays

Converts milliseconds into days.

Type signature

1(milliseconds: number) => number

Examples

1toDays(86400000);
2// ⇒ 1

Questions

• How to convert milliseconds into days?

toHours

Converts milliseconds into hours.

Type signature

1(milliseconds: number) => number

Examples

1toHours(3600000);
2// ⇒ 1

Questions

• How to convert milliseconds into hours?

toISO

Returns an ISO-compliant date-time string.

Type signature

1(x: Date) => string

Examples

1toISO(new Date("2019-04-24T13:54:33.232Z"));
2// ⇒ "2019-04-24T13:54:33.232Z"

Questions

• How to convert Date object to ISO-compliant date string?

toMinutes

Converts milliseconds into minutes.

Type signature

1(milliseconds: number) => number

Examples

1toMinutes(60000);
2// ⇒ 1

Questions

• How to convert milliseconds into minutes?

toSeconds

Converts milliseconds into seconds.

Type signature

1(milliseconds: number) => number

Examples

1toSeconds(1000);
2// ⇒ 1

Questions

• How to convert milliseconds into seconds?

valid

Checks if the given date is present and it is valid.

Type signature

1(date?: unknown) => boolean

Examples

1valid(new Date("2020-01-31T09:52:31.618Z"));
2// ⇒ true

1valid(new Date("2020-01-42:52:31.618Z"));
2// ⇒ false

1valid(new Date("test"));
2// ⇒ false

1valid(undefined);
2// ⇒ false

Questions

• How to check if a Date is valid or not?

debug

assert

Asserts given conditions.

Type signature

1(condition: boolean, callbackOrMessage?: (() => void) | string) => void;
2export declare const throws: (f: () => void) => unknown | undefined;
3export declare const assertNumber: (x?: unknown) => void;
4export declare const assertInteger: (x?: unknown) => void;
5export declare const assertByte: (x?: unknown) => void;
6export declare const assertNormal: (x?: unknown) => void;
7export declare const assertString: (x?: unknown, message?: string) => void;
8export declare const assertIsDefined: (x?: unknown, message?: string) => void;
9export default assert

Examples

1assert(true === false);
2// ⇒ TypeError("Assertion failed!")

Questions

• How to assert a condition?
• How to throw when a condition is not satisfied?

diff

Computes a deep difference between the two values (primitives, objects, arrays, etc.).

Type signature

1(obj1?: unknown, obj2?: unknown) => DiffResult;
2export default diff

Examples

1diff({ a: 1 }, { a: 2 });
2// ⇒ { a: { data: [1, 2], type: '~' }}

Questions

• How to compute a diff?
• How to compute a deep diff?
• How to compute a diff between two objects?
• How to compute a diff between two arrays?

encoding

base64url

decode

Decodes the given Base64URL back into a string.

Type signature

1(text: string, context?: DecodeContext) => string

Examples

1decode("PDw_Pz8-Pg");
2// ⇒ "<<???>>"

Questions

• How to decode Base64URL?

decodeBytes

Decodes the given Base64URL back into a byte array.

Type signature

1(text: string, context?: DecodeContext) => number[]

Examples

1decodeBytes("w4Jnw6vCp20-bBsQfA");
2// ⇒ [0xc2, 0x67, 0xeb, 0xa7, 0x6d, 0x3e, 0x6c, 0x1b, 0x10, 0x7c]

Questions

• How to decode Base64URL into a byte array?

encode

Encodes the given string into Base64URL.

Type signature

1(text: string, context?: EncodeContext) => string

Examples

1encode("<<???>>");
2// ⇒ "PDw_Pz8-Pg"

Questions

• How to encode a string as Base64URL?

encodeBytes

Encodes the given bytes into Base64URL.

Type signature

1(bytes: number[], context?: EncodeContext) => string

Examples

1encodeBytes([0xc2, 0x67, 0xeb, 0xa7, 0x6d, 0x3e, 0x6c, 0x1b, 0x10, 0x7c]);
2// ⇒ "w4Jnw6vCp20-bBsQfA"

Questions

• How to encode bytes as Base64URL?

fromBase64

Converts Base64 string into Base64URL one.

Type signature

1(base64: string) => string

Examples

1fromBase64("PDw/Pz8+Pg==");
2// ⇒ "PDw_Pz8-Pg"

Questions

• How to convert Base64 to Base64URL?

toBase64

Converts Base64URL string into Base64 one.

Type signature

1(base64Url: string) => string

Examples

1toBase64("PDw_Pz8-Pg");
2// ⇒ "PDw/Pz8+Pg=="

Questions

• How to convert Base64URL to Base64?

byteString

from

Converts a string to a byte array.

Type signature

1(byteString: string) => number[]

Examples

1from("PQR");
2// ⇒ [80, 81, 82]

Questions

• How to convert a string into a byte array?

to

Coverts a byte array into a string.

Type signature

1(bytes: number[]) => string

Examples

1to([0x50, 0x51, 0x52]);
2// ⇒ "PQR"

Questions

• How to convert a byte array to string?

file

validName

Checks if the given string is a valid Windows file name.

Type signature

1(name: string) => boolean

Examples

1validName("my:file.png");
2// ⇒ false

1validName("file.txt");
2// ⇒ true

1validName("../file.txt");
2// ⇒ false

1validName("COM1");
2// ⇒ false

Questions

• How to find valid Windows file name?
• How to check if a given string is a legal/valid file name under Windows?

function

compose

Composes multiple functions into a higher-order one. Goes right to left.

Type signature

1<T, TResult>(...fs: ((x: T) => T)[]) => (x: T) => T

Examples

1compose(x => x * x, x => x + 1)(3);
2// ⇒ 16

Questions

• How to compose functions?

constant

Returns the given constant no matter the input.

Type signature

1<T>(x: T) => () => T

Examples

1constant(3)("anything");
2// ⇒ 3

Questions

• How to create a function that always returns the same value despite given arguments?

identity

Always return the given value.

Type signature

1<T>(x: T) => T

Examples

1identity(5);
2// ⇒ 5

1identity("test");
2// ⇒ "test"

Questions

• How to use the identity function?
• Where and why is identity function useful?

memoize

Memoizes the function result so it is not computed for the same parameters. Uses deep equality.

Type signature

1<TResult>(f: (...xs: unknown[]) => TResult) => (...args: unknown[]) => TResult

Examples

1const f = x => { console.log(x); return x + 1; };
2
3const memoized = memoize(f);
4
5memoized(5);
6memoized(5);
7memoized(5);
8memoized(3);

Questions

• How to memoize a function?

memoizeShallow

Memoizes the function result so it is not computed for the same parameters. Uses shallow equality.

Type signature

1<TResult>(f: (...xs: unknown[]) => TResult) => (...args: unknown[]) => TResult

Examples

1const f = ({ x }) => { console.log(x); return x + 1; };
2
3const memoized = memoizeShallow(f);
4
5memoized({ x: 5 });
6memoized({ x: 5 });
7memoized({ x: 5 });
8memoized({ x: 3 });

Questions

• How to memoize a function with shallow equality?

memoizeWith

Memoizes the function result so it is not computed for the same parameters. Uses the given equality function.

Type signature

1<T>(equals: (x: T[], y: T[]) => boolean) => <TResult>(f: (...xs: T[]) => TResult) => (...args: T[]) => TResult

Examples

1const f = ({ x }) => { console.log(x); return x + 1; };
2
3const memoized = memoizeWith((a, b) => a.x === b.x)(f);
4
5memoized({ x: 5 });
6memoized({ x: 5 });
7memoized({ x: 5 });
8memoized({ x: 3 });

Questions

• How to memoize a function with a custom equality function?

noOp

It does exactly nothing.

Type signature

1() => void

Examples

1noOp("anything");
2// ⇒ undefined

Questions

• How to create a function that does nothing?

not

Inverts the given function result.

Type signature

1(f: (...xs: unknown[]) => unknown) => (...args: unknown[]) => boolean

Examples

1not(x > 10)(15);
2// ⇒ true

Questions

• How to invert a boolean function?

pipe

Pipes an input through given functions.

Type signature

1<T>(...fs: ((x: T) => T)[]) => (x: T) => T

Examples

1pipe(x => x * x, x => x + 1)(3);
2// ⇒ 10

Questions

• How to pipe an argument through a function?

when

Runs the given function only when the condition is met.

Type signature

1(predicate: (...xs: unknown[]) => boolean) => (action: (...xs: unknown[]) => unknown) => (...args: unknown[]) => unknown

Examples

1when(x => x > 0)(x => console.log(x))(5);
2when(x => x > 0)(x => console.log(x))(-3);

Questions

• How to run a function only when a condition is satisfied?

whenTrue

Runs the given function only when the condition is exactly true.

Type signature

1(action: (...xs: unknown[]) => unknown) => (...args: unknown[]) => unknown

Examples

1whenTrue(x => console.log(x))(false);
2when(x => x > 0)(x => console.log(x))(true);

Questions

• How to run a function only if its argument is true?
• How to execute function only if a variable is true?

is

array

Checks if the given argument is an array.

Type signature

1(x?: unknown) => boolean

Examples

1array([1, 2, 3]);
2// ⇒ true

1array({ a: 1 });
2// ⇒ false

Questions

• How to check if a given value is an array?

boolean

Checks if the given value is a boolean.

Type signature

1(x?: unknown) => x is boolean

Examples

1boolean(false); // ⇒ true

1boolean(1); // ⇒ false

Questions

• How to check if a given value is a boolean?

byte

Checks if the given value is a byte.

Type signature

1(x?: unknown) => boolean

Examples

1byte(128);
2// ⇒ true

1byte(325);
2// ⇒ false

1byte(65.5);
2// ⇒ false

Questions

• How to check if a given value is a byte?
• How to check if a given number is a byte?

date

Checks if the given value is a Date object.

Type signature

1(x?: unknown) => boolean

Examples

1date(new Date());
2// ⇒ true

1date(123);
2// ⇒ false

Questions

• How to check if a given value is a Date object?

defined

Checks if the given value is defined.

Type signature

1(x?: unknown) => boolean

Examples

1defined(undefined);
2// ⇒ false

1defined(null);
2// ⇒ true

1defined(0);
2// ⇒ true

1defined({ a: 1 });
2// ⇒ true

Questions

• How to check if a given value is defined?
• How to check if a given value is not undefined?

function

Checks if the given value is a function.

Type signature

1(x?: unknown) => x is Function

Examples

1_function(x => x + 5);
2// ⇒ true

Questions

• How to check if a given value is a function?

integer

Checks if the given value is an integer.

Type signature

1(x?: unknown) => boolean

Examples

1integer(5);
2// ⇒ true

1integer(32.5);
2// ⇒ false

Questions

• How to check if a given value is an integer?
• How to check if a given number is an integer?

nonNullable

Checks and asserts the given value is not null or undefined.

Type signature

1<T>(val: T) => val is NonNullable<T>

Examples

1nonNullable(null);
2// ⇒ false

1nonNullable(undefined);
2// ⇒ false

1nonNullable(false);
2// ⇒ true

1nonNullable({ a: 1 });
2// ⇒ true

Questions

• How to check if a given value is non-nullable?
• How to check if a given value is not null?
• How to check if a given value is not undefined?

normal

Checks if the given value is a number in a normal range [0, 1].

Type signature

1(x?: unknown) => boolean

Examples

1normal(0.75);
2// ⇒ true

1normal(-1);
2// ⇒ false

1normal(2.5);
2// ⇒ false

Questions

• How to check if a given value is in 0 to 1 inclusive range?

number

Checks if the given value is a number.

Type signature

1(x?: unknown) => boolean

Examples

1number(0 / 0);
2// ⇒ false

1number(15.6);
2// ⇒ true

Questions

• How to check if a given value is a valid number?
• How to check if a given value is not NaN?
• How to check if a given value is finite?

object

Checks if the given value is an object.

Type signature

1(x?: unknown) => boolean

Examples

1object({ a: 1, b: 2 });
2// ⇒ true

1object([1, 2, 3]);
2// ⇒ false

Questions

• How to check if a given value is an object?

string

Checks if the given value is a string.

Type signature

1(x?: unknown) => x is string

Examples

1string("Test");
2// ⇒ true

1string(['T', 'e', 's', 't']);
2// ⇒ false

Questions

• How to check if a given value is a string?

math

add

Adds two values.

Type signature

1(a: number, b: number) => number

Examples

1add(3, 5);
2// ⇒ 8

Questions

• How to add two values?

average

Calculates the average of the given array of numbers.

Type signature

1(xs?: number[]) => number

Examples

1average([2, 4, 15]);
2// ⇒ 7

Questions

• How to compute the average of an array?

ceilToNearestPowerOfTwo

Finds the nearest power of two greater or equal to the given value.

Type signature

1(x: number) => number

Examples

1ceilToNearestPowerOfTwo(345);
2// ⇒ 512

Questions

• How to get the nearest power of two greater or equal to the given value?

clamp

Clamps the given value to the given range.

Type signature

1(min: number, max: number) => ((x: number) => number)

Examples

1clamp(0, 10)(5);
2// ⇒ 5

1clamp(0, 10)(-5);
2// ⇒ 0

1clamp(0, 10)(15);
2// ⇒ 10

Questions

• How to clamp value to the desired range?
• How to enforce a value to be in a given range?

clampNormal

Clamps the given value to the [0, 1] range.

Type signature

1(x: number) => number

Examples

1clampNormal(0.5);
2// ⇒ 0.5

1clampNormal(-0.5);
2// ⇒ 0

1clampNormal(1.5);
2// ⇒ 1

Questions

• How to clamp value to be in 0 to 1 inclusive range?
• How to clamp value to be in the normal range?

clampPercentage

Clamps the given value to the [0, 100] range.

Type signature

1(x: number) => number

Examples

1clampPercentage(50);
2// ⇒ 50

1clampPercentage(-50);
2// ⇒ 0

1clampPercentage(150);
2// ⇒ 100

Questions

• How to enforce a percentage be between 0% and 100%?

delta

Calculates the absolute distance between given values.

Type signature

1(a: number, b: number) => number

Examples

1delta(-3, 5);
2// ⇒ 8

Questions

• How to calculate an absolute distance between two numbers?

inRectangleRange

Checks if the given value is in the rectangular range of [0, width] and [0, height]

Type signature

1(width: number, height: number) => ((x: number, y: number) => boolean)

Examples

1inRectangleRange(50, 100)(25, 50);
2// ⇒ true

1inRectangleRange(50, 100)(-25, 50);
2// ⇒ false

Questions

• How to check if a point is inside a rectangle defined by width and height?

lerp

Linearly interpolates two given values by the normal value of their distance.

Type signature

1(t: number) => ((a: number, b: number) => number)

Examples

1lerp(0.5)(0, 10);
2// ⇒ 5

1lerp(0)(0, 10);
2// ⇒ 0

1lerp(1)(0, 10);
2// ⇒ 10

Questions

• How to linearly interpolate between two values?
• How to interpolate two numbers?

maximumBy

Calculates the maximum by a given selector.

Type signature

1(f: (x: number) => number) => ((xs: number[]) => number)

Examples

1maximumBy(({ age }) => age)([{ age: 13 }, { age: 20 }, { age: 7 }, { age: 18 }]);
2// ⇒ { age: 20 }

Questions

• How to find a maximum element by a given function?

median

Calculates the median of the values. If there is an even number of items, the average of the middle ones is returned.

Type signature

1(xs?: number[]) => number | undefined

Examples

1median([-5, 3, 2, 29, 43]);
2// ⇒ 3

Questions

• How to compute a median of an array?

minMax

Calculates the minimum and maximum value of the two given values.

Type signature

1([a, b]: [number, number]) => [number, number]

Examples

1minMax([5, 3]);
2// ⇒ [3, 5]

1minMax([3, 5]);
2// ⇒ [3, 5]

Questions

• How to get ordered values where the lower is the first and the higher is the second?

sameSign

Checks if all the given values have the same sign.

Type signature

1(xs: number[]) => boolean

Examples

1sameSign([-1, -2, -3]);
2// ⇒ true

1sameSign([1, 2, -3]);
2// ⇒ false

Questions

• How to check if all values have the same sign?

sign

Calculates the sign of the value and returns -1 for negative values, 1 for positive values and 0 for zeros.

Type signature

1(x: number) => number

Examples

1sign(3);
2// ⇒ 1

1sign(-5);
2// ⇒ 5

1sign(0);
2// ⇒ 0

1sign(-0);
2// ⇒ 0

Questions

• How to get a sign of a number?

standardDeviation

Calculates the standard deviation of the given array of numbers.

Type signature

1(xs: number[], origin?: number) => number

Examples

1standardDeviation([96, 81, 68, 79, 23, 13, 13, 59, 44, 86]);
2// ⇒ (2 * Math.sqrt(10922 / 5)) / 3

Questions

• How to compute a standard deviation of an array?

subtract

Subtracts two values.

Type signature

1(a: number, b: number) => number

Examples

1subtract(3, 5);
2// ⇒ -2

Questions

• How to subtract two numbers?

object

any

Checks if the given object is present and it is not empty (contains at least one entry).

Type signature

1<T>(xs?: GenericObject<T>) => boolean

Examples

1any({ a: 1, b: 2, c: 3 });
2// ⇒ true

1any({ });
2// ⇒ false

1any(null);
2// ⇒ false

1any(undefined);
2// ⇒ false

Questions

• How to check if an object is not empty?
• How to check if an object contains some values?
• How to check if an object is not null or undefined?