Functional Javascript Playground

Functional Programming was always a weird "why would you use this" way of coding as I've primarily been OOP. I set out to change my view on that and learn more about it and when to use it. These are some of the functions I collected/made along the way. They are all ES6/ESM, the parameter order for most lends itself to currying + composing. Still a little iffy on the Hindley-milner signatures so they may be slightly off.

This is very much a WIP

Functions

associate(): Sets the given property and value on the object. Returning a new object.
average(): Averages the given array values
A(): Calls the given function with the given value.
Fork(): Takes a joiner func, and two other funcs and a value. The value is given to both funcs and the results of each of these is given to the joiner func.
I(): Returns the given value.
K(): Takes two values and returns the given first.
OR(): Given two functions that take the same value, returns the first if the result is truthy, otherwise, the second.
T(): Calls the given function with the given value. (Reverse order of apply)
compact(): Removes falsey values from an array.
compose(): Performs right-to-left function composition.
concat(): Concatenates two String|Arrays together. Returns empty array if value arent of the same type or not String|Array.
concatN(): Concatenates N Arrays together.
curry(): Wraps the given function, if the number of provided args is sufficient, call the passed function fn. Otherwise, return a wrapped function fn that expects the rest of the arguments. If you want to curry a function that accepts a variable number of arguments (a variadic function), you can optionally pass the number of arguments to the second parameter arity.
difference(): Returns the difference between two arrays.
distinct(): Returns all of the distinct values of an array.
distinctN(): Returns all of the distinct values of the given arrays.
each(): Applies the given func to each element in the array.
every(): Determines if all element in an array satisfy the given test function
filter(): Filters the array using the given function.
find(): Finds the first element that satisfies the given test func.
flatten(): Flattens single nested array.
isArray(): Determines if the given value is an array.
isFunction(): Determines if the given value is a function.
isNumber(): Determines if the given value is a number.
isObject(): Determines if the given value is an object.
isString(): Determines if the given value is a string.
not(): Negates the given boolean-like value.
tap(): Calls the given function with the given value and returns the value.

associate()

Sets the given property and value on the object. Returning a new object.

Kind: global function
Signature: associate :: String k -> {} -> v -> {k: v}
Example

const obj = associate('c', { a: b }, d)  // { a: b, c: d }

average()

Averages the given array values

Kind: global function
Signature: average :: [Number] -> Number
Example

average([ 1, 2, 3 ]); // 2
average(1, 2, 3); // 2
average(); // 0

A()

Calls the given function with the given value.

Kind: global function
Signature: A :: (a -> b) -> a -> b
Aka: apply

Fork()

Takes a joiner func, and two other funcs and a value. The value is given to both funcs and the results of each of these is given to the joiner func.

Kind: global function
Signature: Fork :: (b -> c -> d) -> (a -> b) -> (a -> c) -> a -> d
Aka: join

I()

Returns the given value.

Kind: global function
Signature: I :: a -> a
Aka: identity

K()

Takes two values and returns the given first.

Kind: global function
Signature: K :: a -> b -> a
Aka: constant

OR()

Given two functions that take the same value, returns the first if the result is truthy, otherwise, the second.

Kind: global function
Signature: OR :: (a -> b) -> (a -> b) -> b
Aka: alternation

T()

Calls the given function with the given value. (Reverse order of apply)

Kind: global function
Signature: T :: a -> (a -> b) -> b
Aka: thrush, applyTo

compact()

Removes falsey values from an array.

Kind: global function
Signature: compact :: [a] -> [a]
Example

compact([ 0, 1, false, 2, '', 3, 'a', 'e' * 23, NaN, 's', 34 ]); // [ 1, 2, 3, 'a', 's', 34 ]
compact(null) // []

compose()

Performs right-to-left function composition.

Kind: global function
Signature: compose :: [(m -> n), ..., (b -> c), (a -> b)] -> a -> n
Example

const addOne = x => x + 1;
const timeTen = x => x * 10;
const addOneTimeTen = compose(timeTen, addOne);
const result = addOneTimeTen(9); // 100

concat()

Concatenates two String|Arrays together. Returns empty array if value arent of the same type or not String|Array.

Kind: global function
Signature: concat :: a -> b -> c
Example

concat('foo', 'bar') // foobar
concat([1, 2], [3, 4]) // [1, 2, 3, 4]

concatN()

Concatenates N Arrays together.

Kind: global function
Signature: concat :: [a] -> [b] -> ...[n] -> [m]
Example

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

curry()

Wraps the given function, if the number of provided args is sufficient, call the passed function fn. Otherwise, return a wrapped function fn that expects the rest of the arguments. If you want to curry a function that accepts a variable number of arguments (a variadic function), you can optionally pass the number of arguments to the second parameter arity.

Kind: global function
Signature: curry :: ((a, b, ..., n) -> m) -> a -> b -> ...n -> m
Example

const add = curry((x, y) => x + y);
const addFiveTo = add(5);
addFiveTo(10); // 15

difference()

Returns the difference between two arrays.

Kind: global function
Signature: difference :: [a] -> [b] -> [c]
Example

difference([ 1, 2, 3 ], [ 1, 2, 4 ]) // [3]
difference([], [ 1, 2, 4 ]) // [ 1, 2, 4 ]
difference([ 1, 2, 3 ], []) // [ 1, 2, 3 ]
difference([ 1, 2, 3 ], null) // [ 1, 2, 3 ]

distinct()

Returns all of the distinct values of an array.

Kind: global function
Signature: distinct :: [a] -> [b]
Example

distinct([ 1, 2, 2, 3, 4, 4, 5 ]) // [ 1, 2, 3, 4, 5 ]

distinctN()

Returns all of the distinct values of the given arrays.

Kind: global function
Signature: distinctN :: [a] -> [b] -> ...[n] -> [m]
Example

distinctN([ 1, 2 ], [ 2, 3, 4 ], [ 4, 5 ]) // [ 1, 2, 3, 4, 5 ]

each()

Applies the given func to each element in the array.

Kind: global function
Signature: each :: (a -> b) -> [c] -> undefined
Example

difference(log, [1, 2, 3])

every()

Determines if all element in an array satisfy the given test function

Kind: global function
Signature: every :: (a -> Bool) -> [a] -> Bool
Aka: all
Example

every(Boolean, [1, 2, 3, 4]) // true
every(Boolean, [1, 2, null, 4]) // false

filter()

Filters the array using the given function.

Kind: global function
Signature: filter :: (a -> Boolean) -> [a] -> [a]
Example

filter(x => x > 5, [1, 2, 3, 5, 6, 7]) // [6, 7]

find()

Finds the first element that satisfies the given test func.

Kind: global function
Signature: find :: (a -> Boolean) -> [a] -> a
Example

find(x => x.score === 5, [{score: 1}, {score: 2}, {score: 5}, {score: 6}, {score: 7}]) // {score: 5}

flatten()

Flattens single nested array.

Kind: global function
Signature: flatten :: [a] -> [a]
Example

flatten([[ 1, 2 ], [ 3, 4 ]];); // [ 1, 2, 3, 4 ]
flatten(null) // []

isArray()

Determines if the given value is an array.

Kind: global function
Signature: isArray :: a -> Boolean
Example

isArray([1, 2, 3])  // true
isArray({ a: 'b' })  // false

isFunction()

Determines if the given value is a function.

Kind: global function
Signature: isFunction :: a -> Boolean
Example

isFunction(() => {})  // true
isFunction([1, 2, 3])  // false

isNumber()

Determines if the given value is a number.

Kind: global function
Signature: isNumber :: a -> Boolean
Example

isNumber(42)  // true
isNumber(8e5)  // true
isNumber(0x2F)  // true
isNumber('foo bar')  // false

isObject()

Determines if the given value is an object.

Kind: global function
Signature: isObject :: a -> Boolean
Example

isObject({ a: 'b' })  // true
isObject([1, 2, 3])  // false

isString()

Determines if the given value is a string.

Kind: global function
Signature: isString :: a -> Boolean
Example

isString('foo bar')  // true
isString({ a: 'b' })  // false

not()

Negates the given boolean-like value.

Kind: global function
Signature: not :: Boolean -> Boolean
Example

not(true); // false
not(false); // true
not(2); // false

tap()

Calls the given function with the given value and returns the value.

Kind: global function
Signature: tap :: (a -> b) -> a -> a
Example

tap(console.log, 'foobar') // foobar

License

FJP is licensed under the MIT license.

fjp

Functional Javascript Playground

This is very much a WIP

Functions

associate()

average()

A()

Fork()

I()

K()

OR()

T()

compact()

compose()

concat()

concatN()

curry()

difference()

distinct()

distinctN()

each()

every()

filter()

find()

flatten()

isArray()

isFunction()

isNumber()

isObject()

isString()

not()

tap()

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