Functions
These are the available library functions.
identity
A function that takes a single parameter and returns it. Essentially a no-op for mapping.
map(identity, [1, 2, 3])or
Given several methods which can return a boolean, create a new predicate which logically "ors" them together.
const isNotATeen = or(lessThan(13), greaterThan(19))
isNotATeen(13)and
Given several methods which can return a boolean, create a new predicate which logically "ands" them together.
const isBetweenFiveAndTen = and(greaterThan(5), lessThan(10))
isBetweenFiveAndTen(7)apply
Given a function that takes multiple parameters, create a new function which takes those parameters as a single tuple instead.
const adder = (a: number, b: string) => a + b
const tupleAdder = apply(adder)
adder(5, 10)
tupleAdder([5, 10])map
Exactly like Array.prototype.map, but functional instead of on the Array prototype.
const adder = map(a => a + 1)
adder([1, 2, 3])chain
Given a value and a function, run the function on the value. This is like map, but for working on any data type. Useful in piped series of computations.
const adder = chain(a => a + 1)
adder(data)constant
Given a value, return a function that will return that value every time it is called.
const alwaysTrue = constant(true)
alwaysTrue()cond
Basically a functional switch statement. Run several predicates to find the correct code path, then transform the data as requested.
const detectRange = cond(
[lessThan(0), () => "Negative"],
[lessThan(100), () => "Less than 100"],
() => "Greater than 100",
)
detectRange(101)equals
Given a value, create a new function which will take a second value and compare their equality. Uses Javascript's === operator.
const equalsFive = equals(5)
equalsFive(5)
equalsFive(10)first
Given an array, return the first value or undefined.
first([1, 2, 3])nth
Given an array, return the nth value or undefined. nth is 1-indexed.
nth([1, 2, 3])(1) // 1index
Given an array, return the index value or undefined. index is 0-indexed.
index([1, 2, 3])(1) // 2last
Given an array, return the last value or undefined.
last([1, 2, 3])rest
Given an array, return every item except the first.
rest([1, 2, 3]) // [2, 3]greaterThan
Create a predicate which checks whether a value is greater than a number.
const greaterThanFive = greaterThan(5)
greaterThanFive(10)
greaterThanFive(1)greaterThanEquals
Create a predicate which checks whether a value is greater than or equal a number.
const greaterThanEqualsFive = greaterThanEquals(5)
greaterThanEqualsFive(10)
greaterThanEqualsFive(1)lessThan
Create a predicate which checks whether a value is less than a number.
const lessThanFive = lessThan(5)
lessThanFive(10)
lessThanFive(1)lessThanEquals
Create a predicate which checks whether a value is less than or equal a number.
const lessThanEqualsFive = lessThanEquals(5)
lessThanEqualsFive(10)
lessThanEqualsFive(1)isBetween
Create a predicate which checks whether a value is between two values.
const isBetween5And10Exclusive = isBetween(5, 10, false)
isBetween5And10Exclusive(10)
const isBetween5And10Inclusive = isBetween(5, 10, true)
isBetween5And10Inclusive(1)pluck
Create a function which grabs a key from an object.
const getName = pluck("name")
getName({ name: "Me", age: Infinity })omit
Create a function which removes a key from an object.
const removeName = omit("name")
removeName({ name: "Me", age: Infinity })pipe
Create a function runs a series of functions in order, passing the result of each step to the next in the series.
const incrementToStringAndRepeat = pipe(
(a: number) => a + 1,
(b: number) => b.toString(),
(c: string) => c + c,
)
incrementToStringAndRepeat(100)Last updated
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