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fjs

Functional JavaScript experiments.

All functions return a new object when making changes

Functional:

Implements functions that work over lists and a simple implementation of partial function application.

var numbers = [1,2,3,4,5];
Functional.map(numbers, function(n) { return n + n; }); // returns [2,4,6,8,10]

var numbers = [1,7,2,3,5,4,10,9,20,13];
Functional.collect(numbers, function(n) { return n < 8; }) // returns [1,7,2,3,5,4]

var numbers = [1,2,3,4,5,6,7,8,9,10];
Functional.foldLeft([1,2,3,4,5,6,7,8,9,10], 0, function(acc, next) { return acc + next; }) // returns 55
Functional.foldRight([1,2,3,4,5,6,7,8,9,10], 0, function(acc, next) { return acc + next; }) // returns 55

Other functions in the Functional namespace are:

  • filter - remove elements that satisfy a predicate
  • sort - sort a list by a function
  • findIndex - find the index of a value using a predicate
  • findIndices - find all indexes of a value using a predicate
  • nub / uniquify - remove duplicates
  • take - take first n elements
  • takeWhile - take elements while a condition is true
  • dropWhile - drop elements while a condition is true
  • head - returns the head of a list
  • tail - returns the tails of a list
  • intersect - returns an intersect of two lists
  • partial - partialy apply a function (apply arguments from left)
  • partialRight - partialy apply a function (apply arguments from right)

Lenses:

Implements simple asymmetric lenses inspired by the Asymmetric Lenses in Scala paper written by Tony Morris

var person = { firstName: "John", lastName: "Doe", address: { street: "Elm", number: 22 }};
var firstNameL = Lenses.attr('firstName'); // creates a lens for the firstName property;
var firstNameLCustom = Lenses.new(function(obj) { return obj.firstName; }, function(obj, value) { obj.firstName = value; }); // Creates a custom lens
firstNameL.get(person); // returns John
firstNameL.set(person, 'Jane') // returns a new object { firstName: "Jane", lastName: "Doe", address: { street: "Elm", number: 22 }};

// We can compose lenses
var addressL = Lenses.attr('address');
var streetL = Lenses.attr('street');
var personStreetL = Lenses.compose(addressL, streetL);
personStreetL.get(person) // returns Elm
personStreetL.set(person, 'Oak') // returns a new object { firstName: "John", lastName: "Doe", address: { street: "Oak", number: 22 }};

Other functions in the Lenses namespace are:

  • fold - folds over a list of lenses resulting in a new lens
  • modify - given a lens and a function applies that function on the property and sets the result
  • id - returns an identity lens

NOTE

Lenses uses an internal copy function that attaches to the Object prototype if the function does not exists. The function uses a simple JSON.parse(JSON.stringify(obj)) to copy an object. This does not copy functions on the object. If that is a problem for you you can provide your own implementation by overriding Object.prototype.copy

I'm open for better suggestions as I'm in no way a JavaScript expert.