Teaching some FP to friends

counter-one.js

var counter = 0

function count() {
  return counter++
}

counter-two.js

function count(x) {
  return x + 1
}

immutable.js

var list = [1, 2, 3]

function addToList(list, value) {
  return [...list, value]
}

list    // => [1, 2, 3]

var newList = addToList(list, 4)

newList // => [1, 2, 3, 4]
list    // => [1, 2, 3]
newList === list // false

increment-list.js

function incrementList(list) {
  for (var i = 0; i < list.length; i++)
    list[i]++
  
  return list
}

map-reduce-three.js

var players = [
  {name: 'João'   , username: 'lubien'   , cards: 6},
  {name: 'Rian'   , username: 'vergachov', cards: 5},
  {name: 'Krishna', username: 'shinark'  , cards: 7}
]

function playerCards(player) { return player.cards }
function sum(x, y) { return x + y }

players
  .map(playerCards) // => [6, 5, 7]
  .reduce(sum)      // => 18

map-reduce-two.js

var players = [
  {name: 'João'   , username: 'lubien'   , cards: 6},
  {name: 'Rian'   , username: 'vergachov', cards: 5},
  {name: 'Krishna', username: 'shinark'  , cards: 7}
]

function playerCards(player) { return player.cards }

players.map(playerCards) // => [6, 5, 7]

map.js

function increment(x) { return x + 1 }

function incrementList(list) { return list.map(increment) }

mul-list.js

function mulList(list) {
  var acc = 1
  
  for (var i = 0; i < list.length; i++)
    acc *= list[i]
  
  return acc
}

mutable.js

var list = [1, 2, 3]

function addToList(list, value) {
  list.push(value)
  return list
}

list    // => [1, 2, 3]

var newList = addToList(list, 4)

newList // => [1, 2, 3, 4]
list    // => [1, 2, 3, 4] !!
newList === list // true

players.js

var players = [
  {name: 'João'   , username: 'lubien'   , cards: 6},
  {name: 'Rian'   , username: 'vergachov', cards: 5},
  {name: 'Krishna', username: 'shinark'  , cards: 7}
]

reduce-one.js

function sum(x, y) { return x + y }
function mul(x, y) { return x * y }

function reduce(list, fn, initial) {
  var acc = initial
  
  for (var i = 0; i < list.length; i++)
    acc = fn(acc, list[i])
  
  return acc
}

function sumList(list) { return reduce(list, sum, 0) }
function mulList(list) { return reduce(list, mul, 1) }

reduce-two.js

function sum(x, y) { return x + y }
function mul(x, y) { return x * y }

function sumList(list) { return list.reduce(sum, 0) }
function mulList(list) { return list.reduce(mul, 1) }

squeeze-list.js

function sum(x, y) { return x + y }
function mul(x, y) { return x * y }

function squeezeList(list, fn, initial) {
  var acc = initial
  
  for (var i = 0; i < list.length; i++)
    acc = fn(acc, list[i])
  
  return acc
}

function sumList(list) { return squeezeList(list, sum, 0) }
function mulList(list) { return squeezeList(list, mul, 1) }

sum-list.js

function sumList(list) {
  var acc = 0
  
  for (var i = 0; i < list.length; i++)
    acc += list[i]
  
  return acc
}

update-list.js

function increment(x) { return x + 1 }

function updateList(list, fn) {
  for (var i = 0; i < list.length; i++)
    list[i] = fn(list[i])
  
  return list
}

function incrementList(list) { return updateList(list, increment) }