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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 one reason or another are not.

Docs

https://smartprocure.github.io/futil-js/

Version History/Changelog

See our changelog

Installing

npm i -S futil or npm i -S futil-js

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

Usage

import * as F from 'futil' or import F from 'futil' or import {x,y,z} from 'futil'

API

Async

promiseProps

{ a: Promise, b: Promise} => Promise<{a: value, b: value}> Like Promise.all, but for objects. Polyfill bluebird Promise.props. Takes an object with promise values and returns a promise that resolves with an object with resolved values instead.

flowAsync

(f1, f2, ...fn) -> (...args) => fn(f2(f1(...args))) Like _.flow, but supports flowing together async and non async methods. If nothing is async, it stays synchronous. Also, it handles awaiting arrays of promises (e.g. from _.map) with Promise.all and objects of promises (e.g. from _.mapValues) with promiseProps. This method generally solves most issues with using futil/lodash methods asynchronously. It's like magic! NOTE: Main gotchas are methods that require early exit like find which can't be automatically async-ified. Also does not handle promises for keys. Use F.resolveOnTree to await more complexly nested promises.

flowAsyncDeep

(f1, f2, ...fn) -> (...args) => fn(f2(f1(...args))) Just like F.flowAsync, except it recurses through return values using F.resolveOnTree instead of just Promise.all or promise.props CAUTION Just like resolveOnTree, this will mutate intermediate results to resolve promises. This is generally safe (and more performant) but might not always be what you expect.

Function

maybeCall

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

callOrReturn

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

boundMethod

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

converge

(f, [g1, g2, ...gn]) -> a -> f([g1(a), g2(a), ...]) http://ramdajs.com/docs/#converge. Note that f is called on the array of the return values of [g1, g2, ...gn] rather than applied to it.

comply (alias: composeApply)

(f, g) -> x -> f(g(x))(x) A combinator that combines compose and apply. f should be a 2 place curried function. Useful for applying comparisons to pairs defined by some one place function, e.g. var isShorterThanFather = F.comply(isTallerThan, fatherOf)

defer

Implement defer, ported from bluebird docs and used by debounceAsync

debounceAsync

A _.debounce for async functions that ensure the returned promise is resolved with the result of the execution of the actual call. Using _.debounce with await or .then would result in the earlier calls never returning because they're not executed - the unit tests demonstate it failing with _.debounce.

flurry

(f1, f2, ...fn) -> f1Arg1 -> f1Arg2 -> ...f1ArgN -> fn(f2(f1)) Flurry is combo of flow + curry, preserving the arity of the initial function. See https://github.com/lodash/lodash/issues/3612.

uncurry

(arg -> arg -> arg) -> (arg, arg, arg) Uncurry allows curried functions to be called with all its arguments at once. Methods curried with lodash or ramda support this call style out of the box, but hand curried methods. This can happen as the result of function composition.

recurry

(n, fn) -> fn(arg1, ...argN) Resets curry arity. Useful in scenarios where you have a curried function whose arity isn't detectable by a lodash or ramda curry - such as one constructed via function composition.

mapArgs

(mapper, fn) -> (...args) -> fn(...args.map(mapper)) Returns a function that applies the mapping operation to all of the arguments of a function. Very similar to _.overArgs, but runs a single mapper on all of the args args.

Iterators

differentLast

handleItem -> handleLastItem -> iterator Creates an iterator that handles the last item differently for use in any function that passes (value, index, list) (e.g. mapIndexed, eachIndexed, etc). Both the two handlers and the result are iterator functions that take (value, index, list).

Logic

overNone

([f1, f2, ...fn]) -> !f1(x) && !f2(x) && ...!fn(x) Creates a function that checks if none of the array of predicates passed in returns truthy for x

ifElse

(condition, onTrue, onFalse, ...x) -> (T(condition)(...x) ? onTrue(...x) : onFalse(...x)) http://ramdajs.com/docs/#ifElse. The transform function T supports passing a boolean for condition as well as any valid argument of _.iteratee, e.g. myBool = applyTest(x); F.ifElse(myBool, doSomething, doSomethingElse);

when

(condition, onTrue, ...x) -> (T(condition)(...x) ? onTrue(...x) : _.identity(...x)) http://ramdajs.com/docs/#when. T extends _.iteratee as above.

unless

(condition, onFalse, ...x) -> (T(condition)(...x) ? _.identity(...x) : onFalse(...x)) http://ramdajs.com/docs/#unless. T extends _.iteratee as above.

whenTruthy

when curried with Boolean

whenExists

when curried with exists

unlessTruthy

unless curried with Boolean

Collection

flowMap

[f1, f2, ...fn] -> _.map(_.flow(fn)) Maps a flow of f1, f2, ...fn over a collection.

findApply

f -> x -> f(find(f, x)) A version of find that also applies the predicate function to the result. Useful when you have an existing function that you want to apply to a member of a collection that you can best find by applying the same function.

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).

insertAtIndex

(index, val, array|string) -> array|string Inserts value into an array or string at index

Example:

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

compactMap

(fn, collection) -> collection Maps fn over the input collection and compacts the result.

sizeBy

(fn, collection) -> number Returns the size of a collection after filtering by fn.

Convert(_In)

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)

getIn

Just like _.get, but with {rearg: false} so the argument order is unchanged from non fp lodash.

hasIn

Just like _.has, but with {rearg: false} so the argument order is unchanged from non fp lodash.

pickIn

Just like _.pick, but with {rearg: false} so the argument order is unchanged from non fp lodash.

includesIn

Just like _.includes, but with {rearg: false} so the argument order is unchanged from non fp lodash.

Convert(_On)

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)

extendOn

Just like _.extend, but with {mutable: true} so it mutates.

defaultsOn

Just like _.defaults, but with {mutable: true} so it mutates.

mergeOn

Just like _.merge, but with {mutable: true} so it mutates.

setOn

Just like _.set, but with {mutable: true} so it mutates.

unsetOn

Just like _.unset, but with {mutable: true} so it mutates.

pullOn

Just like _.pull, but with {mutable: true} so it mutates.

updateOn

Just like _.update, but with {mutable: true} so it mutates.

Convert(_Indexed)

lodash/fp caps iteratees to one argument by default, but sometimes you need the index.

These methods are uncapped versions of lodash's methods.

Any method with uncapped iteratee arguments will use the Indexed convention.

mapIndexed

Just like _.map, but with {cap: false} so iteratees are not capped (e.g. indexes are passed).

findIndexed

Just like _.find, but with {cap: false} so iteratees are not capped (e.g. indexes are passed).

eachIndexed

Just like _.each, but with {cap: false} so iteratees are not capped (e.g. indexes are passed).

reduceIndexed

Just like _.reduce, but with {cap: false} so iteratees are not capped (e.g. indexes are passed).

pickByIndexed

Just like _.pickBy, but with {cap: false} so iteratees are not capped (e.g. indexes are passed).

omitByIndexed

Just like _.omitBy, but with {cap: false} so iteratees are not capped (e.g. indexes are passed).

mapValuesIndexed

Just like _.mapValues, but with {cap: false} so iteratees are not capped (e.g. indexes are passed).

Array

compactJoin

joinString -> [string1, string2, ...stringN] -> string1 + joinString + string2 + joinString ... + stringN Joins an array after compacting. Note that due to the underlying behavior of _.curry no default join value is supported -- you must pass in some string with which to perform the join.

dotJoin

[string1, string2, ...stringN] -> string1 + '.' + string2 + '.' ... + stringN Compacts and joins an array with .

dotJoinWith

filterFunction -> [string1, string2, ...stringN] -> string1 + '.' + string2 + '.' ... + stringN Compacts an array by the provided function, then joins it with .

repeated

[a] -> [a] Returns an array of elements that are repeated in the array.

push

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

moveIndex

(from, to, array) -> array Moves a value from one index to another

mergeRanges

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

Example:

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

isSubset

([a], [a]) -> boolean Determines if an array is a subset of another array.

cycle

[a, b...] -> a -> b Creates a function that takes an element of the original array as argument and returns the next element in the array (with wrapping). Note that (1) This will return the first element of the array for any argument not in the array and (2) due to the behavior of _.curry the created function will return a function equivalent to itself if called with no argument.

arrayToObject

(k, v, [a]) -> { k(a): v(a) } Creates an object from an array by generating a key/value pair for each element in the array using the key and value mapper functions.

keysToObject

(v, [a]) => { a: v(a) } Converts and array of keys to an object using a predicate

zipObjectDeepWith

A version of _.zipObjectDeep that supports passing a function to determine values intead of an array, which will be invoked for each key.

flags

[a, b] -> {a:true, b:true} Converts an array of strings into an object mapping to true. Useful for optimizing includes.

prefixes

['a', 'b', 'c'] -> [['a'], ['a', 'b'], ['a', 'b', 'c']] Returns a list of all prefixes. Works on strings, too. Implementations must guarantee that the orginal argument has a length property.

encoder

string -> {encode: array -> string, decode: string -> array} Creates an object with encode and decode functions for encoding arrays as strings. The input string is used as input for join/split.

dotEncoder

{ encode: ['a', 'b'] -> 'a.b', decode: 'a.b' -> ['a', 'b'] } An encoder using . as the separator

slashEncoder

{ encode: ['a', 'b'] -> 'a/b', decode: 'a/b' -> ['a', 'b'] } An encoder using / as the separator

chunkBy

(([a], a) -> Boolean) -> [a] -> [[a]] Takes a predicate function and an array, and returns an array of arrays where each element has one or more elements of the original array. Similar to Haskell's groupBy.

The predicate is called with two arguments: the current group, and the current element. If it returns truthy, the element is appended to the current group; otherwise, it's used as the first element in a new group.

chunkByValue

f -> [] -> [[], ...] chunkBy when the returned value of an iteratee changes

toggleElementBy

bool -> value -> list -> newList Just like toggleElement, but takes an iteratee to determine if it should remove or add. This is useful for example in situations where you might have a checkbox that you want to represent membership of a value in a set instead of an implicit toggle. Used by includeLens.

toggleElement

(any, array) -> array Removes an element from an array if it's included in the array, or pushes it in if it doesn't. Immutable (so it's a clone of the array).

intersperse

f -> array -> [array[0], f(), array[n], ....) Puts the result of calling f in between each element of the array. f is a standard lodash iterator taking the value, index, and list. If f is not a function, it will treat f as the value to intersperse. See https://ramdajs.com/docs/#intersperse.

Example:

// Example with words (toSentence is basically this flowed into a `_.join('')`):
F.intersperse(
  differentLast(
    () => 'or',
    () => 'or perhaps'
  ),
  ['first', 'second', 'third']
)
// ['first', 'or', 'second', 'or perhaps', 'third']

// Example with React and JSX:
let results = [1, 2, 3]
return (
  <div>
    <b>Results:</b>
    <br />
    {_.flow(
      _.map((x) => <b>{x}</b>),
      F.intersperse(
        F.differentLast(
          () => ', ',
          () => ' and '
        )
      )
    )(results)}
  </div>
)
// Output:
// **Results:**
// **1**, **2** and **3**.

Note: This works great with the differentLast iterator. Also, intersperse can be used with JSX components!

replaceElementBy

(fn(array_element), value, array) -> array Replaces an element in an array with value based on the boolean result of a function fn.

replaceElement

(target, value, array) -> array Replaces all elements equal to target in an array with value.

Object

singleObject

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

singleObjectR

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

chunkObject

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

compactObject

Remove properties with falsey values.

Example:

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

isEmptyObject

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

isNotEmptyObject

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

stripEmptyObjects

Omit properties whose values are empty objects.

Example:

{ a:1, b:{}, c:2 } -> {a:1, c:2}

Note: (TODO rename to omitEmptyObjects)

pickInto

TODO

renameProperty

sourcePropertyName -> targetPropertyName -> sourceObject -> sourceObject Rename a property on an object.

Example:

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

renamePropertyOn

sourcePropertyName -> targetPropertyName -> sourceObject -> sourceObject Rename a property on an object. NOTE:Mutates the object

Example:

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

popProperty

k -> { k: v } -> v Removes a property from an object and returns the removed value. Like F.unsetOn, but returns the removed value instead of the mutated object. Similar to .pop() on arrays, but for objects. Supports nested properties using dot notation. NOTE: Mutates the object. If you don't want mutation, you probably want _.unset for the object or _.get for the value.

unwind

k -> { k: [a, b] } -> [{ k: a }, { k: b }] Just like mongo's $unwind: produces an array of objects from an object and one of its array-valued properties. Each object is constructed from the original object with the array value replaced by its elements. Unwinding on a nonexistent property or a property whose value is not an array returns an empty array.

Example:

F.unwind('b', [{ a: true, b: [1, 2] }])
//=> [{ a: true, b: 1 }, { a: true, b: 2 }]

unwindArray

k -> [{ k: [a, b] }] -> [{ k: a }, { k: b }] Unwinds an array of objects instead of a single object, as you might expect if you're used to mongo's $unwind. Alias for (key, data) => _.flatMap(F.unwind(key), data)

Example:

F.unwindArray('b', [
  { a: true, b: [1, 2] },
  { a: false, b: [3, 4] },
])
//=> [
//=>  { a: true, b: 1 },
//=>  { a: true, b: 2 },
//=>  { a: false, b: 3 },
//=>  { a: false, b: 4 },
//=> ]

flattenObject

Flatten an object with the paths for keys.

Example:

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

unflattenObject

Unlatten an object with the paths for keys.

Example:

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

matchesSignature

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

matchesSome

Similar to _.matches, except it returns true if 1 or more object properties match instead of all of them. See https://github.com/lodash/lodash/issues/3713.

compareDeep

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

mapProp

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}

getOrReturn

_.get that returns the target object if lookup fails

alias

_.get that returns the prop if lookup fails

aliasIn

Flipped alias

cascade

A _.get that takes an array of paths (or functions to return values) and returns the value at the first path that matches. Similar to _.overSome, but returns the first result that matches instead of just truthy (and supports a default value)

cascadeIn

Flipped cascade

cascadeKey

A _.get that takes an array of paths and returns the first path that matched

cascadePropKey

A _.get that takes an array of paths and returns the first path that exists

cascadeProp

A _.get that takes an array of paths and returns the first value that has an existing path

unkeyBy

newKey -> {a:x, b:y} -> [{...x, newKey: a}, {...y, newKey: b}] Opposite of _.keyBy. Creates an array from an object where the key is merged into the values keyed by newKey.

Example:

F.unkeyBy('_key')({ a: { status: true}, b: { status: false }) -> [{ status: true, _key: 'a' }, { status: false, _key: 'b' }]

Note: Passing a falsy value other than undefined for newKay will result in each object key being pushed into its corresponding return array member with itself as value, e.g. F.unkeyBy('')({ a: { status: true}, b: { status: false }) -> [{ status: true, a: 'a' }, { status: false, b: 'b' }]. Passing undefined will return another instance of F.unkeyBy.

simpleDiff

(from, to) -> simpleDiff Produces a simple flattened (see flattenObject) diff between two objects. For each (flattened) key, it produced a from and a to value. Note that this will omit any values that are not present in the deltas object.

simpleDiffArray

(from, to) -> [simpleDiffChanges] Same as simpleDiff, but produces an array of { field, from, to } objects instead of { field: { from, to } }

diff

(from, to) -> diff Same as simpleDiff, but also takes in count deleted properties. Note: We're considering not maintaining this in the long term, so you might probably have more success with any existing library for this purpose.

diffArray

(from, to) -> [diffChanges] Same as simpleDiffArray, but also takes in count deleted properties. Note: We're considering not maintaining this in the long term, so you might probably have more success with any existing library for this purpose.

pickOn

A _.pick that mutates the object

mergeAllArrays

Like _.mergeAll, but concats arrays instead of replacing. This is basically the example from the lodash mergeAllWith docs.

invertByArray

{ a: [x, y, z], b: [x] } -> { x: [a, b], y: [a], z: [a] } Similar to _.invert, but expands arrays instead of converting them to strings before making them keys.

stampKey

key -> { a: { x: 1 }, b: { y: 2 } } -> { a: { x: 1, key: 'a' }, b: { y: 2, key: 'b' } } Iterates over object properties and stamps their keys on the values in the field name provided.

omitNil

_.omitBy using _.isNil as function argument.

omitNull

_.omitBy using _.isNull as function argument.

omitBlank

_.omitBy using F.isBlank as function argument.

omitEmpty

_.omitBy using _.isEmpty as function argument.

mergeOverAll

([f, g], ...args) -> {...f(...args), ...g(...args)} Composition of _.over and _.mergeAll. Takes an array of functions and an arbitrary number of arguments, calls each function with those arguments, and merges the results. Can be called with mergeOverAll([f, g], x, y) or mergeOverAll([f, g])(x, y). Note: For functions that do not return objects, _.merge's behavior is followed: for strings and arrays, the indices will be converted to keys and the result will be merged, and for all other primitives, nothing will be merged.

mergeOverAllWith

(customizer, [f, g], ...args) -> {...f(...args), ...g(...args)} A customizable mergeOverAll that takes a function of the form (objValue, srcValue) -> newValue as its first argument; see _.mergeWith. Both the customizer and array of functions can be partially applied.

mergeOverAllArrays

([f, g], ...args) -> {...f(...args), ...g(...args)} A customized mergeOverAll that applies the array-merging behavior of mergeAllArrays.

getWith

(x -> y) -> k -> {k: x} -> y Like _.get, but accepts a customizer function which is called on the value to transform it before it is returned. Argument order is (customizer, path, object).

expandObject

(transform: obj -> newObj) -> obj -> { ...obj, ...newObj } Accepts a transform function and an object. Returns the result of applying the transform function to the object, merged onto the original object. expandObject(f, obj) is equivalent to mergeOverAll([_.identity, f], obj).

expandObjectBy

key -> (transform: x -> newObj) -> (obj: { key: x }) -> { ...obj, ...newObj } Expands an object by transforming the value at a single key into a new object, and merging the result with the original object. Similar to expandObject, but the argument order is (key, transform, object), and the transform function is called on the value at that key instead of on the whole object.

commonKeys

(x, y) -> [keys] Takes two objects and returns the keys they have in common

firstCommonKey

(x, y) -> key Takes two objects and returns the first key in y that x also has

updateIfExists

(path, updater, object) -> object Like _.update, but does not call the iteratee if the path is missing on the object

updateIfExistsOn

(path, updater, object) -> object Like F.updateOn, but does not call the iteratee if the path is missing on the object Mutates the object

updatePathsOn

({ path: transform }, target) -> obj Similar to ramda's R.evolve, but supports lodash iteratees and nested paths. Applies transforms to the target object at each path. The transform function is called with the value at that path, and the result is set at that path. Transforms are not called for paths that do not exist in the target object. Transform functions support lodash iteratee shorthand syntax. Deep paths are supported by nesting objects and by dotted the keys

Note: Mutates the target object for performance. If you don't want this, use updatePaths or clone first.

updateAllPathsOn

({ path: transform }, target) -> obj Similar to ramda's R.evolve, but supports lodash iteratees and nested paths. Applies transforms to the target object at each path. The transform function is called with the value at that path, and the result is set at that path. Transforms are called for paths that do not exist in the target object. Transform functions support lodash iteratee shorthand syntax. Deep paths are supported by nesting objects and by dotted the keys

Note: Mutates the target object for performance. If you don't want this, use updateAllPaths or clone first.

updateAllPaths

({ path: transform }, target) -> obj Similar to ramda's R.evolve, but supports lodash iteratees and nested paths. Applies transforms to the target object at each path. The transform function is called with the value at that path, and the result is set at that path. Transforms are called for paths that do not exist in the target object. Transform functions support lodash iteratee shorthand syntax. Deep paths are supported by nesting objects and by dotted the keys

Note Deep clones prior to executing to avoid mutating the target object, but mutates under the hood for performance (while keeping it immutable at the surface). If you're doing this in a place where mutating is safe, you might want F.updateAllPathsOn to avoid the _.deepClone

updatePaths

({ path: transform }, target) -> obj Similar to ramda's R.evolve, but supports lodash iteratees and nested paths. Applies transforms to the target object at each path. The transform function is called with the value at that path, and the result is set at that path. Transforms are not called for paths that do not exist in the target object. Transform functions support lodash iteratee shorthand syntax. Deep paths are supported by nesting objects and by dotted the keys

Note Deep clones prior to executing to avoid mutating the target object, but mutates under the hood for performance (while keeping it immutable at the surface). If you're doing this in a place where mutating is safe, you might want F.updatePathsOn to avoid the _.deepClone

matchesBy

(criteria: object, object: object) -> boolean Takes a criteria object and an object to test against it, and returns true if all the values in the criteria match the values in the object Criteria values can be functions or values to compare against Supports dot notation for deep paths

matchesBySome

(criteria: object, object: object) -> boolean Takes a criteria object and an object to test against it, and returns true if some of the values in the criteria match the values in the object Criteria values can be functions or values to compare against Supports dot notation for deep paths

String

wrap

(pre, post, content) -> pre + content + post Wraps a string with pre and post unless content is nil (and replaces )

parens

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

trimStrings

Maps _.trim through all the strings of a given object or array.

autoLabel

string -> string Converts strings like variable names to labels (generally) suitable for GUIs, including support for acronyms and numbers. It's basically _.startCase with acronym and number support.

autoLabelOption

string -> {value:string, label:string} Creates a {value, label} which applies autoLabel the string parameter on puts it on the label property, with the original on the value property. You can also pass in an object with value or with both value and label.

autoLabelOptions

[string] -> [{value:string, label:string}] Applies autoLabelOption to a collection. Useful for working with option lists like generating select tag options from an array of strings.

toSentenceWith

(separator, lastSeparator, array) => string Just like toSentence, but with the ability to override the separator and lastSeparator

Example:

(' - ', ' or ', ['a', 'b', 'c']) -> 'a - b or c'

toSentence

array => string Joins an array into a human readable string. See https://github.com/epeli/underscore.string#tosentencearray-delimiter-lastdelimiter--string

Example:

['a', 'b', 'c'] -> 'a, b and c'

uniqueStringWith

(fn, array) -> string -> string Allows passing a "cachizer" function (array -> object) to override the way uniqueString's initial array is converted into a cache object. Can be curried to create a custom uniqueString function, eg: let myUniqueString = uniqueStringWith(myFunc)

Like uniqueString, the resulting deduplication function exposes cache and clear() properties.

Example:

let uniqueStringStripDigits = uniqueStringWith(
  _.countBy(_.replace(/(\d+)$/, ''))
)
let dedupe = uniqueStringStripDigits(['foo', 'foo42', 'foo3000'])
dedupe('foo') //-> 'foo3'
uniqueStringWith(_.identity, dedupe.cache)('foo') //-> 'foo4'

uniqueString

array -> string -> string Returns a function that takes a string and de-duplicates it against an internal cache. Each time this function is called, the resulting deduplicated string is added to the cache. Exposes cache and clear() properties to read and clear the cache, respectively.

Example:

let dedupe = uniqueString()
_.map(dedupe, ['foo', 'foo', 'foo']) //-> ['foo', 'foo1', 'foo2']
dedupe.cache //-> { foo: 3, foo1: 1, foo2: 1 }
dedupe.clear()
dedupe.cache //-> {}
dedupe('foo') //-> 'foo'

crunchWhitespace

string -> string Replaces whitespace substrings with a single space and trims leading/trailing whitespace

Regex

testRegex

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

makeRegex

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

makeAndTest

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

matchAllWords

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

matchAnyWord

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

allMatches

regex -> string -> [{text: string, start: number, end: number}] Returns an array of matches with start/end data

Example:

F.allMatches(/a/g, 'vuhfaof') -> [ { text: 'a', start: 4, end: 5 } ]

postings

regex -> string -> [[number, number]] Returns an array of postings (position ranges) for a regex and string to test, e.g. F.postings(/a/g, 'vuhfaof') -> [[4, 5]]

postingsForWords

words -> string -> [[[number, number]]] Takes a string of words and a string to test, and returns an array of arrays of postings for each word.

Example:

F.postingsForWords('she lls', 'she sells sea shells')
// [
//   [[0, 3], [14, 17]]
//   [[6, 9], [17, 20]]
// ]

highlight

start -> end -> pattern -> input -> highlightedInput Wraps the matches for pattern found in input with the strings start and end. The pattern argument can either be a string of words to match, or a regular expression.

Example:

let braceHighlight = F.highlight('{', '}')
braceHighlight('l o', 'hello world') //-> "he{llo} w{o}r{l}d"
braceHighlight(/l+\w/, 'hello world') //-> "he{llo} wor{ld}"

Math

greaterThanOne

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

Lang

Language level utilities

isPromise

x -> bool A utility that checks if the argument passed in is of type promise

throws

Just throws whatever it is passed.

tapError

Tap error will run the provided function and then throw the first argument. It's like _.tap for rethrowing errors.

exists (alias: isNotNil)

Negated _.isNil

isMultiple

(Array<T> | string | {length}) -> bool Returns true if the input has a length property > 1, such as arrays, strings, or custom objects with a lenth property

append

(a, b) => b + a A curried, flipped _.add. The flipping matters for strings, e.g. F.append('a')('b') -> 'ba'

isBlank

x -> bool Designed to determine if something has a meaningful value, like a ux version of truthiness. It's false for everything except null, undefined, '', [], and {}. Another way of describing it is that it's the same as falsiness except 0 and false are truthy and {} is falsey. Useful for implementing "required" validation rules.

isNotBlank

x -> bool Opposite of isBlank

isBlankDeep

f -> x -> bool Recurses through an object's leaf properties and passes an array of booleans to the combinator, such as _.some, _.every, and F.none

Lens

A lens is a getter and setter pair. You use them to write code that needs to read and write a value (like a method to flip a boolean switch, or a React component that reads and writes some state) without worrying about the implementation.

Functions that operate on lenses can handle a few different "shorthand" structures. This is similar to lodash's _.iteratee (which allows their methods to treat strings, objects, or functions as shorthand predicates)

A lens can be any of these formats:

({ get, set }) An object with a get function and set function. Found in: MobX "boxed observables" Example Usage: F.flip({ get, set })

([value, setter]) An array of the value and a setter function to change it. Found in: React's useState hook Example Usage: F.flip([value, setter])

(lookup, object) A lookup path and object pair e.g. ('key', object). The lookup path is anything you can pass to _.get (so nested paths with . or as an array are supported) Found in: MobX observable objects, native JS objects Example Usage: F.flip(lookup, object)

(x => {}) A function which returns the value when called with no arguments and sets it when called with one. Found in: Knockout observables, jQuery plugin APIs Example Usage: F.flip(x => {})

(getter, setter) A getter and setter pair. Found in: Anywhere you have a getter and setter function Example Usage: F.flip(getter, setter)

Note: Setter methods are generally mutable (unlike Ramda's lenses, for example).

We've included a few example "bindings" on F.domLens. These take a lens and return an object that's useful in a DOM context (like React or raw JS). In React terms, they're methods that generate the props you'd use to do two way binding to a lens.

functionLens

Takes a value and returns a function lens for that value. Mostly used for testing and mocking purposes.

objectLens

Takes a value and returns a object lens for that value. Mostly used for testing and mocking purposes.

set

propertyValue -> Lens -> object.propertyName Sets the value of the lens, regardless of its format

fnToObj

Converts a function lens an object lens. Mostly used for testing and mocking purposes.

objToFn

Converts an object lens to a function lens. Mostly used for testing and mocking purposes.

lensProp

propertyName -> object -> { get: () -> object.propertyName, set: propertyValue -> object.propertyName } 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. Supports deep paths like lodash get/set. You typically won't use this directly since it is supported implicitly.

lensOf

Takes an object and returns an object with lenses at the values of each path. Basically mapValues(lensProp). Typically you would use the implicit (key, object) format instead.

includeLens

value -> arrayLens -> includeLens An include lens represents membership of a value in a set. It takes a value and lens and returns a new lens - kind of like a "writeable computed" from MobX or Knockout. The view and set functions allow you to read and write a boolean value for whether or not a value is in an array. If you change to true or false, it will set the underlying array lens with a new array either without the value or with it pushed at the end.

view

Lens -> object.propertyName Gets the value of the lens, regardless of its format

views

Lens -> (() -> object.propertyName) Returns a function that gets the value of the lens, regardless of its format

sets

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

setsWith

Takes an iteratee and lens and creates a function that will set a lens with the result of calling the iteratee with the provided value

flip

Takes a lens and negates its value

on

Returns a function that will set a lens to true

off

Returns a function that will set a lens to false

domLens.value

lens -> {value, onChange} Takes a lens and returns a value/onChange pair that views/sets the lens appropriately. onChange sets with e.target.value (or e if that path isn't present).

Example:

let Component = () => {
  let state = React.useState('')
  return <input {...F.domLens.value(state)}>
}

domLens.checkboxValues

(value, lens) -> {checked, onChange} Creates an includeLens and maps view to checked and set to onChange (set with e.target.checked or e if that path isn't present)

domLens.hover

lens -> { onMouseEnter, onMouseLeave } Takes a lens and returns on onMouseEnter which calls on on the lens and onMouseLeave which calls off. Models a mapping of "hovering" to a boolean.

domLens.focus

lens -> { onFocus, onBlur } Takes a lens and returns on onFocus which calls on on the lens and onBlur which calls off. Models a mapping of "focusing" to a boolean.

domLens.targetBinding

field -> lens -> {[field], onChange} Utility for building lens consumers like value and checkboxValues

domLens.binding

(field, getValue) -> lens -> {[field], onChange} Even more generic utility than targetBinding which uses getEventValue to as the function for a setsWith which is mapped to onChange.

stateLens

([value, setValue]) -> lens Given the popularity of React, we decided to include this little helper that converts a useState hook call to a lens. Ex: let lens = stateLens(useState(false)). You generally won't use this directly since you can pass the [value, setter] pair directly to lens functions

Aspect

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 it assumes 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.

There are a few basic aspects included on F.aspects (E.g. var loggedFunc = F.aspect(F.aspects.logs)(func)) 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.

aspect

{options} -> f -> aspectWrapped(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 is equivalent to the original function for all arguments.

Options supports the following parameters:

Example:

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

aspectSync

This is a synchronous version of aspect, for situations when it's not desirable to await a method you're adding aspects to. The API is the same, but things like onError won't work if you pass an async function to the aspect.

aspects.logs

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

aspects.error

Captures any exceptions thrown and set it on an error error it puts on state

aspects.errors

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

aspects.status

Adds a status property that is set to processing before the wrapped function runs and succeeded when it's done or failed if it threw an exception. Also adds shortcuts on state for processing, succeeded, and failed, which are booleans which are based on the value of status. Also adds a setStatus method which is used internally to update these properties.

aspects.deprecate

Utility for marking functions as deprecated - it's just a before with a console.warn. Takes the name of thing being deprecated, optionally deprecation version, and optionally an alternative and returns a higher order function which you can wrap deprecated methods in. This is what's used internally to mark deprecations. Includes a partial stack trace as part of the deprecation warning.

aspects.clearStatus

Sets status to null after provided timeout (default is 500ms) elapses. If a null timeout is passed, it will never set status to null.

aspects.concurrency

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

aspects.command

Flows together status, clearStatus, concurrency, and error, taking extend and timeout as optional parameters to construct the aspect

Tree

All tree functions take a traversal function so that you can customize how to traverse arbitrary nested structures.

Note: Be careful about cyclic structures that can result in infinite loops, such as objects with references to itself. There are cases where you'd intentionally want to visit the same node multiple times, such as traversing a directed acyclic graph (which would work just fine and eventually terminate, but would visit a node once for each parent it has connected to it) - but it's up to the user to be sure you don't create infinite loops.

isTraversable

node -> bool A default check if something can be traversed - currently it is arrays and plain objects.

traverse

node -> [...childNodes] The default traversal function used in other tree methods if you don't supply one. It returns false if it's not traversable or empty, and returns the object if it is.

walk

traverse -> (pre, post=_.noop) -> tree -> x A depth first search which visits every node returned by traverse recursively. Both pre-order and post-order traversals are supported (and can be mixed freely). walk also supports exiting iteration early by returning a truthy value from either the pre or post functions. The returned value is also the return value of walk. The pre, post, and traversal functions are passed the current node as well as the parent stack (where parents[0] is the direct parent).

walkAsync

traverse -> (pre, post=_.noop) -> async tree -> x A version of walk which supports async traversals.

transformTree

traverse -> _iteratee -> tree -> newTree Structure preserving pre-order depth first traversal which clones, mutates, and then returns a tree. Basically walk with a _.cloneDeep first (similar to a tree map because it preserves structure). _iteratee can be any suitable argument to _.iteratee https://lodash.com/docs/4.17.5#iteratee

reduceTree

traverse -> (accumulator, initialValue, tree) -> x Just like _.reduce, but traverses over the tree with the traversal function in pre-order.

writeTreeNode

Default writeNode for mapTree. It writes the node to the parent at the given index. Using the traversal function with tree iteratee properties to find children.

mapTree

(traverse, writeNode) -> f -> tree -> newTree Structure preserving tree map! writeNode informs how to write a single node, but the default will generally work for most cases. The iteratee is passed the standard node, index, parents, parentIndexes args and is expected to return a transformed node.

mapTreeLeaves

(traverse, writeNode) -> f -> tree -> newTree Like mapTree, but only operates on lead nodes. It is a convenience method for mapTree(next, writeNode)(F.unless(next, mapper), tree)

treeToArrayBy

traverse -> f -> tree -> [f(treeNode), f(treeNode), ...] Like treeToArray, but accepts a customizer to process the tree nodes before putting them in an array. The customizer is passed the standard node, index, parents, parentIndexes args and is expected to return a transformed node. It's _.map for trees - but it's not called treeMap because it does not preserve the structure as you might expect map to do. See mapTree for that behavior.

treeToArray

traverse -> tree -> [treeNode, treeNode, ...] Flattens the tree nodes into an array, simply recording the node values in pre-order traversal.

leavesBy

traverse -> f -> tree -> [f(treeNode), f(treeNode), ...] Like leaves, but accepts a customizer to process the leaves before putting them in an array.

leaves

traverse -> tree -> [treeNodes] Returns an array of the tree nodes that can't be traversed into in pre-order.

treeLookup

(traverse, buildIteratee) -> ([_iteratee], tree) -> treeNode Looks up a node matching a path, which defaults to lodash iteratee but can be customized with buildIteratee. The _iteratee members of the array can be any suitable arguments for _.iteratee https://lodash.com/docs/4.17.5#iteratee

keyTreeByWith

traverse -> transformer -> _iteratee -> tree -> result Similar to a keyBy (aka groupBy) for trees, but also transforms the grouped values (instead of filtering out tree nodes). The transformer takes three args, the current node, a boolean of if the node matches the current group, and what group is being evaluated for this iteratee. The transformer is called on each node for each grouping. _iteratee is any suitable argument to _.iteratee, as above.

treeKeys

(x, i, xs, is) => [i, ...is] A utility tree iteratee that returns the stack of node indexes

treeValues

(x, i, xs) => [x, ...xs] A utility tree iteratee that returns the stack of node values

treePath

(build, encoder) -> treePathBuilderFunction Creates a path builder for use in flattenTree. By default, the builder will look use child indexes and a dotEncoder. Encoder can be an encoding function or a futil encoder (an object with encode and decode functions)

propTreePath

prop -> treePathBuilderFunction Creates a path builder for use in flattenTree, using a slashEncoder and using the specified prop function as an iteratee on each node to determine the keys.

flattenTree

traverse -> buildPath -> tree -> result Creates a flat object with a property for each node, using buildPath to determine the keys. buildPath takes the same arguments as a tree walking iteratee. It will default to a dot tree path.

findNode

(traverse) -> (iteratee, tree) -> treeNode Finds the first node matching the iteratee in pre-order traversal. The iteratee can be any suitable argument to _.iteratee https://lodash.com/docs/4.17.5#iteratee

resolveOnTree

(traverse, writeNode) -> tree -> result Resolves all Promise nodes of a tree and replaces them with the result of calling .then Exposed on F.tree as resolveOn CAUTION This method mutates the tree passed in. This is generally safe and more performant (and can be intuited from the On convention in the name), but it's worth calling out.

tree

(traverse, buildIteratee, writeNode) -> { walk, walkAsync, transform, reduce, toArrayBy, toArray, leaves, leavesBy, lookup, keyByWith, traverse, flatten, flatLeaves, map, mapLeaves, resolveOn } Takes a traversal function and returns an object with all of the tree methods pre-applied with the traversal. This is useful if you want to use a few of the tree methods with a custom traversal and can provides a slightly nicer api. Exposes provided traverse function as traverse