It.js

It.js is a library to make it easier to create accessor/iterator functions, for use with things like _.map, _.filter, _.sortBy, _.each, and so on... It complements nicely with Underscore.js.

This library is inspired by the article Combinator Recipes for Working With Objects in JavaScript by Reginald Braithwaite, but I want it to look more fluent and chainable.

tldr

In short, this library allows you to write this:

It.send('toLowerCase')

instead of this:

function(name) { return name.toLowerCase() }

And this:

It.instantiate(Status)

instead of this:

function(json) { return new Status(json) }

They are chainable, so you can also write things like this:

It.get('first').get('length')

instead of this:

function(person) { return person.first.length }

example.js

var _ = require('underscore')
var It = require('./')

var numbers = [3, 1, 4, 1, 5]
var strings = ['this', 'is', 'a', 'Book']

It

It provides an identity function, just like _.identity, but much shorter.

This maps an array with itself... Pretty useless

console.log(_.map(numbers, It))

[ 3, 1, 4, 1, 5 ]

This gets a sorted copy of an array. We just sort by itself! (This is nice since underscore has only _.sortBy, but not _.sort)

console.log(_.sortBy(numbers, It))
console.log(_.sortBy(strings, It))

[ 1, 1, 3, 4, 5 ]
[ 'Book', 'a', 'is', 'this' ]

.get

.get returns the value of a property. Here's where things get interesting...

Let's create a function that returns the length of a string (or an array, or whatever object that has .length property).

// equivalent to function(x) { return x.length }
var getLength = It.get('length')

We can use it to sort the strings by their length.

console.log(_.sortBy(strings, getLength))

[ 'a', 'is', 'this', 'Book' ]

.send

Use .send(...) to call a method on an object.

// equivalent to function(x) { return x.toUpperCase() }
var upcase = It.send('toUpperCase')

With this, we can map all these strings to uppercase:

console.log(_.map(strings, upcase))

[ 'THIS', 'IS', 'A', 'BOOK' ]

And with this, case-insensitive sorting is easy:

console.log(_.sortBy(strings, upcase))

[ 'a', 'Book', 'is', 'this' ]

Chaining

Of course, all of these are chainable.

// equivalent to function(x) { return x.substr(0, 1).toUpperCase() }
var firstCharacterCapitalized = It.send('substr', 0, 1).send('toUpperCase')

Get the first character of each string, capitalized.

console.log(_.map(strings, firstCharacterCapitalized))

[ 'T', 'I', 'A', 'B' ]

Now, let's move on and try to use chaining to do something more practical...

Here we have a list of people. (name generation thanks to chance.js)

var addressBook = [
  { first: 'Sifwa', last: 'Duhav', phone: '(416) 984-4454' },
  { first: 'Moc', phone: '(898) 983-5755' },
  { first: 'Diblacbo', last: 'Li', phone: '(258) 838-8314' },
  { first: 'Betu', last: 'Jol', phone: '(219) 234-9591' },
  { first: 'Fuhetu', last: 'Ra', phone: '(631) 437-2332' }
]

Let's sort them by the length of first name!

// equivalent to function(x) { return x.first.length }
var firstNameLength = It.get('first').get('length')

console.log(_.sortBy(addressBook, firstNameLength))

[ { first: 'Moc', phone: '(898) 983-5755' },
  { first: 'Betu', last: 'Jol', phone: '(219) 234-9591' },
  { first: 'Sifwa', last: 'Duhav', phone: '(416) 984-4454' },
  { first: 'Fuhetu', last: 'Ra', phone: '(631) 437-2332' },
  { first: 'Diblacbo', last: 'Li', phone: '(258) 838-8314' } ]

.set

.set(property, value) sets a property on an object. The result of this operation will be the invoked object, so you can chain more operations (something like .set('a','b').set('c','d')).

Let's set everyone's score to zero! Yes, scores in an address book!

_.each(addressBook, It.set('score', 0))
console.log(addressBook)

[ { first: 'Sifwa',
    last: 'Duhav',
    phone: '(416) 984-4454',
    score: 0 },
  { first: 'Moc', phone: '(898) 983-5755', score: 0 },
  { first: 'Diblacbo',
    last: 'Li',
    phone: '(258) 838-8314',
    score: 0 },
  { first: 'Betu', last: 'Jol', phone: '(219) 234-9591', score: 0 },
  { first: 'Fuhetu', last: 'Ra', phone: '(631) 437-2332', score: 0 } ]

.maybe

.maybe(func) invokes a passed function with current value only if the current value is truthy.

In the address book above, Moc doesn't have a last name. Without .maybe(), we will end up calling .toLowerCase() on undefined, and an Error will be thrown.

We want to call .toLowerCase() only when we have something to call on.

// equivalent to function(x) { return x.last && x.last.toLowerCase() }
var lastNameLowered = It.get('last').maybe(It.send('toLowerCase'))
console.log(_.map(addressBook, lastNameLowered))

[ 'duhav', undefined, 'li', 'jol', 'ra' ]

Then you can filter out falsy value by using _.filter(..., It).

console.log(_.filter(_.map(addressBook, lastNameLowered), It))

[ 'duhav', 'li', 'jol', 'ra' ]

.or

Instead of using .maybe, we can use .or to put a default value.

var lastNameLowered2 = It.get('last').or('None').send('toLowerCase')
console.log(_.map(addressBook, lastNameLowered2))

[ 'duhav', 'none', 'li', 'jol', 'ra' ]

.instantiate

.instantiate(Constructor) can be used to quickly map things into an instance.

Here we have a Person class.

function Person(info) {
  this.info = info
}
Person.prototype.getName = function() {
  return this.info.first + ' ' + this.info.last
}
Person.prototype.greet = function() {
  console.log('Hello! I am "' + this.getName() + '"')
}

We can map everyone in the address book into a new Person instance!

// equivalent to function(x) { return new Person(x) }
var people = _.map(addressBook, It.instantiate(Person))
_.each(people, It.send('greet'))

Hello! I am "Sifwa Duhav"
Hello! I am "Moc undefined"
Hello! I am "Diblacbo Li"
Hello! I am "Betu Jol"
Hello! I am "Fuhetu Ra"

It.self

You can use It.self instead of It to create a function that uses the value of this instead of the value of passed argument.

You can use it to quickly make an accessor function

Person#getFirstName returns the first name.

// equivalent to function() { return this.info.first }
Person.prototype.getFirstName = It.self.get('info').get('first')

This function takes a last name, and returns a name suffix. No need to check of null here, we'll let .maybe do it.

function initial(string) {
  return ' ' + string.substr(0, 1) + '.'
}

Person#getLastInitial returns the initial of last name. If the person does not have last name, then return empty string.

// equivalent to function() { return (this.info.last && initial(this.info.last)) || '' }
Person.prototype.getLastInitial = It.self.get('info').get('last').maybe(initial).or('')

We can then redefine the getName method to make use of them:

Person.prototype.getName = function() {
  return this.getFirstName() + this.getLastInitial()
}

_.each(people, It.send('greet'))

Hello! I am "Sifwa D."
Hello! I am "Moc"
Hello! I am "Diblacbo L."
Hello! I am "Betu J."
Hello! I am "Fuhetu R."

.compose

You can use .derive to compose your own functionality.

Here we have these vectors...

var vectors = [
  { x: 1, y: 5 }, { x: 5, y: 1 }, { x: 2, y: -3 }
]

We also have a square function...

function square(x) {
  return x * x
}

Let's get the square of x and y components of these vectors!

console.log(_.map(vectors, It.get('x').compose(square)))
console.log(_.map(vectors, It.get('y').compose(square)))

[ 1, 25, 4 ]
[ 25, 1, 9 ]

You can also use .compose to chain functions together.

var test = { a: { b: 1 }, b: { a: 2 } }
var getA = It.get('a')
var getB = It.get('b')
var getAB = getA.compose(getB)
var getBA = getB.compose(getA)
console.log(test)
console.log(getA(test))
console.log(getB(test))
console.log(getAB(test))
console.log(getBA(test))

{ a: { b: 1 }, b: { a: 2 } }
{ b: 1 }
{ a: 2 }
1
2

Let's bring back that array of Person instances, and the firstNameLength function we created earlier before.

The firstNameLength function works with JSON data, not Person instances. Luckily, the Person class stores the original JSON data in the .info property. So we can still sort these people by their first name length.

_.each(_.sortBy(people, It.get('info').compose(firstNameLength)), It.send('greet'))

Hello! I am "Moc"
Hello! I am "Betu J."
Hello! I am "Sifwa D."
Hello! I am "Fuhetu R."
Hello! I am "Diblacbo L."

.tap

.tap invokes the passed function with the current value, and returns the current value.

log the numbers and while mapping to get the squares

console.log(numbers)
console.log(_.map(numbers, It.tap(console.log).compose(square)))

[ 3, 1, 4, 1, 5 ]
3
1
4
1
5
[ 9, 1, 16, 1, 25 ]

make everyone greet while mapping to get their first name

console.log(_.map(people, It.tap(It.send('greet')).send('getFirstName')))

Hello! I am "Sifwa D."
Hello! I am "Moc"
Hello! I am "Diblacbo L."
Hello! I am "Betu J."
Hello! I am "Fuhetu R."
[ 'Sifwa', 'Moc', 'Diblacbo', 'Betu', 'Fuhetu' ]

License

MIT Licensed