fun-ts

A collection of utilities for functional programming in TS fully typed

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Modules

Core
Array
Condition
Math
String

Core

log

Function that logs one parameter with a label and returns back the logged parameter.

log = <T>(label: string) => (toLog: T): T

E.g.

const contacts = compose(map((user) => user.name), log('Favourite users'), filter(favouritesOnly));

compose

Function for composing multiple functions. First function (listed last) can have multiple input params. Other functions must follow 1 input, 1 output. It is safely typed and if function types do not link together a custom TypeError type is returned instead.

compose<T, U>((arg: any) => T, ...((arg: any) => any), (...args: U) => any): (...args: U) => T

E.g.

const maxCelsiusNumberToFahrenheitString = compose(append('°F'), numberToString, add(32), multiply(1.8), Math.max);
// typeof maxCelsiusNumberToFahrenheitString = (...numbers: number[]) => string

const incorrectLink = compose(append('°F'), add(32), multiply(1.8), Math.max);
// typeof incorrectLink = TypeError<
//    "Can't pass result into next function at position (from right)", 4,
//    (b: number) => number, "--> into -->", (appendee: string) => string
// >

pipe

Function for creating function from piping through multiple functions. First function can have multiple input params. Other functions must follow 1 input, 1 output. It is safely typed and if function types do not link togerther a custom TypeError type is returned instead.

pipe<T, U>((...args: U) => any, ...((arg: any) => any), (arg: any) => T): (...args: U) => T

E.g.

const minFahrenheitNumberToCelsiusString = pipe(Math.min, subtract(32), divide(1.8), numberToString, append('°C'));
// typeof minFahrenheitNumberToCelsiusString = (...numbers: number[]) => string

const incorrectLink = pipe(Math.min, subtract(32), divide(1.8), append('°C'));
// typeof incorrectLink = TypeError<
//    "Can't pass result into next function at position", 4,
//    (b: number) => number, "--> into -->", (appendee: string) => string
// >

Array

every

Function that returns true if all elements of the array match the predicate.

every = <T>(
    predicate: (value: T, index: number, array: T[]) => boolean,
) => (array: T[]): boolean;

E.g.

const test = [1, 2, 3, '4'];
every((n) => typeof n === 'number')(test); // => false ('4' is not a type of number)

filter

Function for filtering an array.

filter = <T>(
    predicate: (value: any, index: number, array: any[]) => value is T,
) => (array: any[]): T[];

E.g.

const numbers = [-3, -2, -1, 0, 1, 2, 3];
const positiveOnly = (n: number) => n > 0;
const filterPositiveOnly = filter(positiveOnly);
filterPositiveOnly(numbers); // => [1, 2, 3];

find

Function to find first entry that matches the predicate.

find = <T>(
    predicate: (value: T, index: number, array: T[]) => boolean,
) => (array: T[]): T | undefined;

E.g.

const users = [{ id: 1, name: 'Frank' }, ...];
const byId = (idToFind: number) => ({ id }) => id === idToFind;
const findById = (idToFind: number) => find(byId(idToFind));

const user1 = findById(1)(users);

findIndex

Function to findex the index of first entry that matches the predicate.

findIndex = <T>(
    predicate: (value: T, index: number, array: T[]) => boolean,
) => (array: T[]): number;

E.g.

const users = [{ id: 1, name: 'Frank' }, ...];
const indexOfFrank = findIndex(({ name }) => name === 'Frank')(users);

flat

Function to flatten the array.

flat = (array: any[]) => array.flat();

E.g.

const numbers = [[1], [2], [3]];
flat(numbers); // => [1, 2, 3];

forEach

Function to run a function for each element of the array.

forEach = <T>(
    eachFunction: (value: T, index: number, array: T[]) => void,
) => (array: T[]): undefined;

E.g.

const users = [{ id: 1, name: 'Frank' }, ...];
const logUsers = forEach(log('User:'));
logUsers(users);

map

Function to map one array into another array.

map = <T, U>(
    mappingFunction: (value: T, index: number, array: T[]) => U,
) => (array: T[]): U[];

E.g.

const numbers = [1, 2, 3, 4];
const toDouble = map((n) => n * 2);
toDouble(numbers); // => [2, 4, 6, 8];

reduce

Function to reduce array to accumulator.

reduce = <T, U>(
    reducer: (accumulator: U, currentValue: T, index: number, array: T[]) => U,
) => (initialValue: U) => (array: T[]): U;

E.g.

const sum = reduce((acc: number, value: number) => acc + value)(0);
const product = reduce((acc: number, value: number) => acc * value)(1);
const numbers = [1, 2, 3, 4];
sum(numbers); // => 10
product(numbers); // => 24

reduceRight

Function to reduce array to accumulator going from the end of array.

reduceRight = <T, U>(
    rightReducer: (accumulator: U, currentValue: T, index: number, array: T[]) => U,
) => (initialValue: U) => (array: T[]): U;

reverse

Function to reverse an array. It returns a new array and does not modify the original.

reverse = <T>(array: T[]) => [...array].reverse();

E.g.

const numbers = [1, 2, 3];
reverse(numbers); // => [3, 2, 1];

some

Function that returns true if any of the elements of the array match the predicate.

some = <T>(
    predicate: (value: T, index: number, array: T[]) => boolean,
) => (array: T[]): boolean;

E.g.

const test = [1, 2, 3, '4'];
some((n) => typeof n === 'string')(test); // => true ('4' is a type of string)

Condition

and

Function that returns true if all passed conditions are true.

and = (...conditions: boolean[]): boolean;

E.g.

and(true, true, false); // => false

cond

Main function for writing conditional statements.

cond = (condition: boolean) => (truthyBranch: B1) => (falsyBranch: B2): ReturnType<B1 | B2>;

E.g.

cond(isDefined(array))(() => array)(() => []);

isDefined

Function that returns true if the passed param is not undefined.

isDefined = <T>(value: T | undefined): value is T;

E.g.

isDefined(0); // => true
isDefined(undefined); // => false

isFalsy

Function that returns true if the passed param is false when cast to boolean.

isFalsy = (value: any): boolean;

E.g.

isFalsy('Hello'); // => false
isFalsy(0); // => true

isNotNull

Function that returns true if the passed param is not null.

isNotNull = <T>(value: T | null): value is T;

E.g.

isNotNull(0); // => true
isNotNull(null); // => false

isNotNullNorUndefined

Function that returns true if the passed param is not null nor undefined.

isNotNullNorUndefined = <T>(value: T | null | undefined): value is T;

E.g.

isNotNullNorUndefined(0); // => true
isNotNullNorUndefined(null); // => false
isNotNullNorUndefined(undefined); // => false

isTruthy

Function that returns true if the passed param is true when cast to boolean.

isTruthy = (value: any): boolean;

E.g.

isTruthy('Hello'); // => true
isTruthy(1); // => true

not

Function that negates passed boolean value.

const not = (value: boolean): boolean;

E.g.

not(true); // => false
not(false); // => true

or

Function that returns true if any of the params is true.

or = (...conditions: boolean[]): boolean;

E.g.

or(true, false, false); // => true

switches

Function to do more complex branching.

switches = (switchCase: Case, ...cases: Case[]): any;
switchCase = (condition: boolean) => (branch: () => T): Case<T>;
defaultCase = (branch: () => T): Case<T>;

E.g.

import { switches, switchCase, defaultCase } from 'fun-ts/condition';

// onUp, onDown, onLeft, onRight return true if they can process keydown, false otherwise.

const processedKeyDown = switches(
    switchCase(keyCode === UP)(onUp),
    switchCase(keyCode === DOWN)(onDown),
    switchCase(keyCode === LEFT)(onLeft),
    switchCase(keyCode === RIGHT)(onRight),
    defaultCase(() => false),
);

xor

Function that returns true if one and only one if the params is true.

xor = (...conditions: boolean[]): boolean;

E.g.

xor(true, false, false); // => true
xor(false, true, true); // => false

Math

add

Function to sum two numbers.

add = (a: number) => (b: number): number; // a + b

E.g.

const numbers = [1, 2, 3];
map(add(5))(numbers); // => [6, 7, 8];

divide

Function to divide second number by first number.

divide = (a: number) => (b: number): number; // b / a

E.g.

const numbers = [10, 20, 30];
map(divide(10))(numbers); // => [1, 2, 3];

modulo

Function to get modulo.

modulo = (a: number) => (b: number): number; // b % a

E.g.

const numbers = [1, 2, 3];
map(modulo(2))(numbers); // => [1, 0, 1];

multiply

Function to multiply two numbers.

multiply = (a: number) => (b: number): number; // a * b

E.g.

const numbers = [1, 2, 3];
map(multiply(10))(numbers); // => [10, 20, 30];

product

Function to get a product of an array.

product = (array: number[]): number;

E.g.

const numbers = [1, 2, 3, 4];
product(numbers); // => 24

subtract

Function to subtract first number from the second number.

subtract = (a: number) => (b: number): number; // b - a

E.g.

const numbers = [6, 7, 8];
map(subtract(5))(numbers); // => [1, 2, 3];

sum

Function to get a sum of an array.

sum = (array: number[]): number;

E.g.

const number = [1, 2, 3, 4];
sum(numbers); // => 10

String

join

Function to join an array of strings with a separator to a single string.

join = (separator: string) => (array: string[]): string;

E.g.

const numbers = [1, 2, 3];
join(', ')(map(toString)(numbers)); // => '1, 2, 3'

split

Function to split a string by divider.

split = (divider: string) => (s: string): string[];

E.g.

const numbers = '1, 2, 3, 4';
split(', ')(numbers); // => ['1', '2', '3', '4'];

toString

Function to convert anything with .toString() function to string.

interface ToString { toString: () => string }

toString = <T extends ToString>(x: T): string;

E.g.

const numbers = [1, 2, 3, 4];
map(toString)(numbers); // => ['1', '2', '3', '4'];

@salik1992/fun-ts

fun-ts

Coverage

Modules

Core

log

compose

pipe

Array

every

filter

find

findIndex

flat

forEach

map

reduce

reduceRight

reverse

some

Condition

and

cond

isDefined

isFalsy

isNotNull

isNotNullNorUndefined

isTruthy

not

or

switches

xor

Math

add

divide

modulo

multiply

product

subtract

sum

String

join

split

toString

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