A collection of F(unctional) Util(ities). Resistance is futile.

Mostly, these are generic utilities that could conceivably be part of a library like lodash/fp, but for some reason or other are not.

See our changelog

npm i -S futil-js

This package requires lodash/fp, so make sure that's available in your app.

import * as f from futil-js or import {x,y,z} from futil-js

The syntax: import f from futil-js is not currently supported.

(fn, a, b) -> fn(a, b) If fn is a function, call the function with the passed-in arguments. Otherwise, return false.

(fn, a, b) -> fn(a, b) If fn is a function, call the function with the passed-in arguments. Otherwise, return fn.

([f, g]) -> !f(x) && !g(x) Creates a function that checks if none of the predicates return truthy when invoked with the arguments it receives.

(a, Monoid f) -> f[a] :: f a Binds a function of an object to it's object.

...fns:functions -> map:function Runs a map function that runs a flow of the functions passed in to this method.

These are conversions of lodash fp methods.

getIn, includesIn, pickIn lodash/fp is great, but sometimes the curry order isn't exactly what you want. These methods provide alternative orderings that are sometimes more convenient. The idea of In methods is to name them by convention, so when ever you need a method that actually takes the collection first (e.g. a get where the data is static but the field is dynamic), you can just add In to the end (such as getIn which takes the object first)

extendOn, defaultsOn lodash/fp likes to keep things pure, but sometimes JS can get pretty dirty. These methods are alternatives for working with data that--for whatever the use case is--needs to be mutable Any methods that interact with mutable data will use the On convention (as it is some action occuring On some data)

join:string -> data:array -> result:string Joins an array after compacting.

data:array -> result:string Compacts and joins an array with '.'

data:array -> result:array Returns an array of elements that are repeated in the array.

([[], [], []]) -> [[], []] Takes any number of ranges and return the result of merging them all.

Example: [[0,7], [3,9], [11,15]] -> [[0,9], [11,15]]

insertAtIndex -> (index, val, string) -> string Insert a string at a specific index.

Example: (1, '123', 'hi') -> 'h123i'

(val, array) -> array Return the array with the val pushed

[a, b...] -> a -> b Creates a function that always return the element next to the one received, based on an input previously received.

(k, v) -> {k: v} Creates an object with a key and value.

(v, k) -> {k: v} Flipped version of singleObject.

({a, b}) -> [{a}, {b}] Breaks an object into an array of objects with one key each.

Remove properties with falsey values.

Example: ({ a: 1, b: null, c: false }) -> {a:1}

Check if the variable is an empty object ({}).

Check if the variable is not an empty object ({}).

Omit properties whose values are empty objects.

Example: { a:1, b:{}, c:2 } -> {a:1, c:2} (TODO remame to omitEmptyObjects)

Checks if an object's property is equal to a value.

Returns true if object keys are only elements from signature list. (but does not require all signature keys to be present)

TODO

from:string -> to:string: -> target:object -> result:object Rename a property on an object.

Example: renameProperty('a', 'b', {a:1}) -> {b:1)

Just like mongo's $unwind.

Example: { x:['a','b'], y:1 } -> [{ x:'a', y:1 }, { x:'b', y:1 }]

Flatten an object with the paths for keys.

Example: { a: { b: { c: 1 } } } => { 'a.b.c' : 1 }.

Unlatten an object with the paths for keys.

Example: { 'a.b.c' : 1 } => { a: { b: { c: 1 } } }.

Deprecated in favor of lodash update Applies a map function at a specific path

Example: mapProp(double, 'a', {a: 2, b: 1}) -> {a: 4, b: 1}.

'asdf' -> '(asdf)' Wraps a string in parenthesis.

regex -> string -> bool Just like ramda test, creates a function to test a regex on a string.

options:string -> string -> regex A curried implementation of RegExp construction.

options:string -> string -> (string -> bool) Makes and tests a RegExp with makeRegex and testRegex.

string -> string -> bool Returns true if the second string matches any of the words in the first string.

string -> string -> bool Returns true if the second string matches all of the words in the first string.

regex -> string -> [Range:[number, number]] Returns an array of postings (position ranges) for a regex and string to test.

start:string -> end:string -> postings:[Range:[number, number]] -> input:string -> string Highlights postings in a string wrapping in start and end.

Example: ('<b>', '<b>', [[0,1]], 'hi') -> '<b>h</b>i'

number -> bool Returns true if number is greater than one.

Language level utilities

Just throws whatever it is passed.

map :: (a -> b) -> [a] -> [b] Maps a function over an iterable. Works by default for Arrays and Plain Objects.

deepMap :: (a -> b) -> [a] -> [b] Maps a function over a recursive iterable. Works by default for nested Arrays, nested Plain Objects and mixed nested Arrays and Plain Objects. Also works for any other iterable data type as long as two other values are sent: a mapping function, and a type checker (See the unit tests for deepMap).

A lens is a getter and setter pair, which can be used to interface to some part of an object graph. Methods that operate on lenses can encapsulate common operations independent of knowledge of their surrounding context. Unlike some traditional functional lenses (like Ramda's), the set methods here are generally mutable.

An object lens is simply an object that has a get and set function. An example of this is a mobx boxed observable.

A function lens is a lense expressed as a single function that takes the value to set or returns the current value if nothing is passed. Examples of this in the wild are knockout observables and jquery plugin api style methods.

The utilities in this library expect can accept either kind of lens, and utilities are provided to seamless convert between the two.

Lens stubs are primarily a reference implementation, but are useful for testing and mocking purposes

Takes a value and returns a function lens for that value

Takes a value and returns a object lens for that value

Methods to convert between lens types

Converts a function lens an object lens

Converts an object lens to a function lens

This the first main way you'll generally interact with the lens API

lensProp :: string -> object -> { get: () -> T, set: T -> T } Creates an object lens for a given property on an object. .get returns the value at that path and set places a new value at that path

{a: T, b: T} -> {a:ObjectLens, b:ObjectLens} Takes an object and returns an object with lenses at the values of each path. Basically mapValues(lensProp).

Lens -> T Gets the value of the lens, regardless of if it's a function or object lens

Lens -> (() -> T) Returns a function that gets the value of the lens, regardless of if it's a function or object lens

T -> Lens -> T Sets the value of the lens, regardless of if it's a function or object lens

Creates a function that will set a lens with the provided value

Takes a lens and negates its value

Returns a function that will set a lens to true

Returns a function that will set a lens to false

Aspects provide a functional oriented implementation of Aspect Oriented Programming. An aspect wraps a function and allows you run code at various points like before and after execution. Notably, aspects in this library allow you to have a shared state object between aspects and are very useful for automating things like status indicators, etc on functions.

There is a lot of prior art in the javascript world, but most of them assume a vaguely object oriented context. The implementation in futil-js is done in just 20 lines of code and seems to capture all of the use cases of AOP.

Note: To do OO style AOP with this these aspects, just use lodash's _.update method and optionally boundMethod from futil if this matters

Caveat: While you can and should compose (or _.flow) aspects together, don't put non aspects in the middle of the composition. Aspects rely on a .state property on the wrapped function that they propagate through, but the chain will break if a non-aspect is mixed in between. Additionally, if you need external access to the state, make sure the aspects are the outer most part of the composition so the .state property will be available on the result of the composition.

aspect: {options} -> f -> () The aspect api takes an options object and returns a function which takes a function to wrap. The wrapped function will be decorated with a state object and should referentially transparent (e.g. it can be called in the same way as the function it's replacing).

Options supports the following parameters:

Example Usage:

let exampleAspect = aspect({
  before: () => console.log('pre run'),
  after: () => console.log('post run')
})
let f = () => console.log('run')
let wrapped = exampleAspect(f)
wrapped()
// Logs to the console:
// pre run
// run
// post run

There are a few basic aspects included because they seem to be universally useful. All of the provided aspects take an extend function to allow customizing the state mutation method (e.g. in mobx, you'd use extendObservable). If null, they default to defaultsOn from futil-js - check the unit tests for example usage.

Logs adds a logs array to the function state and just pushes in results on each run

Captures any exceptions thrown and pushes them into an errors array it puts on state

Adds a processing flag that is set to true before the wrapped function runs and false when it's done

Prevents a function from running if it's state has processing set to true at the time of invocation