DevNexus 2017: Functional Programming Basics in ES6

Transcript

1. FUNCTIONAL PROGRAMMING Jeremy Fairbank blog.jeremyfairbank.com @elpapapollo / jfairbank BASICS IN ES6
2. sigient.com
4. ¯\_(ϑ)_/¯ WHAT IS FUNCTIONAL PROGRAMMING?
5. ¯\_(ϑ)_/¯ WHY FUNCTIONAL PROGRAMMING?
7. Domain to Range
10. Domain Range
11. CALCULUS
12. PRINCIPLES
13. PURE & DECLARATIVE PREDICTABLE
14. IMMUTABLE STATE SAFE
15. FIRST CLASS STATE TRANSPARENT
16. COMPOSABLE FIRST CLASS CLOSURES MODULAR
17. ES2015 (ES6)
18. let age = 10; age = 11; const name = 'Tucker'; name = 'Sally'; All good Syntax error
19. const add = (x, y) => { return x + y; }; const identity = x => x;
20. const add = (x, y) => { return x + y; }; const identity = x => x;
21. const add = (x, y) => { return x + y; }; const identity = x => x;
22. const add = (x, y) => { return x + y; }; const identity = x => x;
23. const add = (x, y) => { return x + y; }; const identity = x => x;
24. const add = (x, y) => { return x + y; }; const identity = x => x;
25. const array = (...elements) => { return elements; }; array(1, 2, 3); // [1, 2, 3]
26. const array = (...elements) => { return elements; }; array(1, 2, 3); // [1, 2, 3]
27. const array = (...elements) => { return elements; }; array(1, 2, 3); // [1, 2, 3]
28. const array = (...elements) => { return elements; }; array(1, 2, 3); // [1, 2, 3]
29. const log = (...args) => { console.log(...args); }; log('Hello', 'DevNexus'); // Hello DevNexus
30. const log = (...args) => { console.log(...args); }; log('Hello', 'DevNexus'); // Hello DevNexus
31. const langs = [ 'JavaScript', 'Elm', 'Haskell', ]; const [js, ...rest] = langs; js === 'JavaScript'; rest[0] === 'Elm'; rest[1] === 'Haskell';
32. const langs = [ 'JavaScript', 'Elm', 'Haskell', ]; const [js, ...rest] = langs; js === 'JavaScript'; rest[0] === 'Elm'; rest[1] === 'Haskell';
33. const langs = [ 'JavaScript', 'Elm', 'Haskell', ]; const [js, ...rest] = langs; js === 'JavaScript'; rest[0] === 'Elm'; rest[1] === 'Haskell';
34. const langs = [ 'JavaScript', 'Elm', 'Haskell', ]; const [js, ...rest] = langs; js === 'JavaScript'; rest[0] === 'Elm'; rest[1] === 'Haskell';
35. const head = ([x]) => x; head([1, 2, 3]) === 1;
36. const head = ([x]) => x; head([1, 2, 3]) === 1;
37. const head = ([x]) => x; head([1, 2, 3]) === 1;
38. const greet = (name, greeting = 'Hi') => { console.log(greeting, name); }; greet('DevNexus', 'Hello'); // Hello DevNexus greet('Atlanta'); // Hi Atlanta
39. const greet = (name, greeting = 'Hi') => { console.log(greeting, name); }; greet('DevNexus', 'Hello'); // Hello DevNexus greet('Atlanta'); // Hi Atlanta
40. const greet = (name, greeting = 'Hi') => { console.log(greeting, name); }; greet('DevNexus', 'Hello'); // Hello DevNexus greet('Atlanta'); // Hi Atlanta
41. const greet = (name, greeting = 'Hi') => { console.log(greeting, name); }; greet('DevNexus', 'Hello'); // Hello DevNexus greet('Atlanta'); // Hi Atlanta
42. Object.assign( {}, { hello: 'Atlanta' }, { hi: 'DevNexus' } ); // { // hello: 'Atlanta', // hi: 'DevNexus' // }
43. Object.assign( {}, { hello: 'Atlanta' }, { hi: 'DevNexus' } ); // { // hello: 'Atlanta', // hi: 'DevNexus' // }
44. Object.assign( {}, { hello: 'Atlanta' }, { hi: 'DevNexus' } ); // { // hello: 'Atlanta', // hi: 'DevNexus' // }
45. class Point { constructor(x, y) { this.x = x; this.y = y; } moveBy(dx, dy) { this.x += dx; this.y += dy; } } function Point(x, y) { this.x = x; this.y = y; } Point.prototype.moveBy = function(dx, dy) { this.x += dx; this.y += dy; };
46. PURE
47. const add = (x, y) => x + y; add(2, 3) === 5; add(2, 3) === 5; add(2, 3) === 5;
48. const add = (x, y) => x + y; add(2, 3) === 5; add(2, 3) === 5; add(2, 3) === 5; Referentially transparent
49. × let name = 'Jeremy'; const getName = () => name; const setName = (newName) => { name = newName; }; const printUpperName = () => { console.log(name.toUpperCase()); };
50. × let name = 'Jeremy'; const getName = () => name; const setName = (newName) => { name = newName; }; const printUpperName = () => { console.log(name.toUpperCase()); };
51. × let name = 'Jeremy'; const getName = () => name; const setName = (newName) => { name = newName; }; const printUpperName = () => { console.log(name.toUpperCase()); };
52. × let name = 'Jeremy'; const getName = () => name; const setName = (newName) => { name = newName; }; const printUpperName = () => { console.log(name.toUpperCase()); };
53. describe('api', () => { beforeEach(() => mockConsoleLog()); afterEach(() => restoreConsoleLog()); it('sets and prints the name', () => { printUpperName(); expect(console.log).calledWith('JEREMY'); setName('Jet'); printUpperName(); expect(console.log).calledWith('JET'); }); }); ×
54. HIDDEN STATE IS UNCERTAIN STATE
55. const upperName = (name) => name.toUpperCase(); describe('api', () => { it('returns an uppercase name', () => { expect(upperName('Jeremy')).to.equal('JEREMY'); expect(upperName('Jet')).to.equal('JET'); }); }); ✓
56. HOW TO ACHIEVE THE RESULT IMPERATIVE
57. function doubleNumbers(numbers) { const doubled = []; const l = numbers.length; for (let i = 0; i < l; i++) { doubled.push(numbers[i] * 2); } return doubled; } doubleNumbers([1, 2, 3]); // [2, 4, 6]
58. DECLARE WHAT THE DESIRED RESULT IS DECLARATIVE
59. function doubleNumbers(numbers) { return numbers.map(n => n * 2); } doubleNumbers([1, 2, 3]); // [2, 4, 6]
60. function doubleNumbers(numbers) { return numbers.map(n => n * 2); } doubleNumbers([1, 2, 3]); // [2, 4, 6]
61. 1 2 3 numbers.map(n => n * 2) 2 4 6 Domain Range
62. CREATE STATE, DON’T MUTATE IT IMMUTABLE
63. const hobbies = [ 'programming', 'reading', 'music', ]; const firstTwo = hobbies.splice(0, 2); console.log(firstTwo); // ['programming', 'reading'] console.log(hobbies); // ['music']
64. const hobbies = [ 'programming', 'reading', 'music', ]; const firstTwo = hobbies.splice(0, 2); console.log(firstTwo); // ['programming', 'reading'] console.log(hobbies); // ['music'] Slight typo + mutability
65. Object.freeze Immutable.js
66. const hobbies = Object.freeze([ 'programming', 'reading', 'music', ]); const firstTwo = hobbies.splice(0, 2); // TypeError
67. const hobbies = Object.freeze([ 'programming', 'reading', 'music', ]); const firstTwo = hobbies.splice(0, 2); // TypeError
68. FREE YOUR STATE
69. class Point { constructor(x, y) { this.x = x; this.y = y; } moveBy(dx, dy) { this.x += dx; this.y += dy; } } const point = new Point(0, 0); point.moveBy(5, 5); point.moveBy(-2, 2); console.log([point.x, point.y]); // [3, 7] ×
70. const createPoint = (x, y) => Object.freeze([x, y]); const movePointBy = ([x, y], dx, dy) => { return Object.freeze([x + dx, y + dy]); }; let point = createPoint(0, 0); point = movePointBy(point, 5, 5); point = movePointBy(point, -2, 2); console.log(point); // [3, 7] ✓ (*or object-oriented without mutation)
71. const createPoint = (x, y) => Object.freeze([x, y]); const movePointBy = ([x, y], dx, dy) => { return Object.freeze([x + dx, y + dy]); }; let point = createPoint(0, 0); point = movePointBy(point, 5, 5); point = movePointBy(point, -2, 2); console.log(point); // [3, 7] ✓ (*or object-oriented without mutation)
72. const createPoint = (x, y) => Object.freeze([x, y]); const movePointBy = ([x, y], dx, dy) => { return Object.freeze([x + dx, y + dy]); }; let point = createPoint(0, 0); point = movePointBy(point, 5, 5); point = movePointBy(point, -2, 2); console.log(point); // [3, 7] ✓ (*or object-oriented without mutation)
73. const createPoint = (x, y) => Object.freeze([x, y]); const movePointBy = ([x, y], dx, dy) => { return Object.freeze([x + dx, y + dy]); }; let point = createPoint(0, 0); point = movePointBy(point, 5, 5); point = movePointBy(point, -2, 2); console.log(point); // [3, 7] ✓ (*or object-oriented without mutation)
74. PROS SAFETY FROM ACCIDENTAL MUTATION FREE UNDO/REDO LOGS — REDUX EXPLICIT FLOW OF DATA CONCURRENCY SAFETY
75. CONS VERBOSE MORE OBJECT CREATION* MORE GARBAGE COLLECTION* MORE MEMORY USAGE* *Alleviated with libs like Immutable.js
76. FIRST CLASS FUNCTIONS
77. const multiply = (x, y) => x * y; function add(x, y) { return x + y; } const addAlias = add; const evens = [1, 2, 3].map(n => n * 2);
78. const multiply = (x, y) => x * y; function add(x, y) { return x + y; } const addAlias = add; const evens = [1, 2, 3].map(n => n * 2);
79. const multiply = (x, y) => x * y; function add(x, y) { return x + y; } const addAlias = add; const evens = [1, 2, 3].map(n => n * 2);
80. const multiply = (x, y) => x * y; function add(x, y) { return x + y; } const addAlias = add; const evens = [1, 2, 3].map(n => n * 2);
81. ENCAPSULATION CLOSURES
82. const createAdder = (x) => { return (y) => x + y; }; const add3 = createAdder(3); add3(2) === 5; add3(3) === 6;
83. const createAdder = (x) => { return (y) => x + y; }; const add3 = createAdder(3); add3(2) === 5; add3(3) === 6;
84. const request = (options) => { return fetch(options.url, options) .then(resp => resp.json()); }; const usersPromise = request({ url: '/users', headers: { 'X-Custom': 'mykey' } }); const tasksPromise = request({ url: '/tasks', headers: { 'X-Custom': 'mykey' } });
85. const request = (options) => { return fetch(options.url, options) .then(resp => resp.json()); }; const usersPromise = request({ url: '/users', headers: { 'X-Custom': 'mykey' } }); const tasksPromise = request({ url: '/tasks', headers: { 'X-Custom': 'mykey' } }); Repetitive
86. const createRequester = (options) => { return (otherOptions) => { return request(Object.assign( {}, options, otherOptions )); }; }; const customRequest = createRequester({ headers: { 'X-Custom': 'mykey' } }); const usersPromise = customRequest({ url: '/users' }); const tasksPromise = customRequest({ url: '/tasks' });
87. const createRequester = (options) => { return (otherOptions) => { return request(Object.assign( {}, options, otherOptions )); }; }; const customRequest = createRequester({ headers: { 'X-Custom': 'mykey' } }); const usersPromise = customRequest({ url: '/users' }); const tasksPromise = customRequest({ url: '/tasks' });
88. FOUNDATION FOR HIGHER ORDER PATTERNS FIRST CLASS CLOSURES
89. PARTIAL APPLICATION
90. const createAdder = (x) => { return (y) => x + y; }; const createRequester = (options) => { return (otherOptions) => { return request(Object.assign( {}, options, otherOptions )); }; }; RECALL
91. const add = (x, y) => x + y; const add3 = partial(add, 3); add3(2) === 5;
92. const add = (x, y) => x + y; const add3 = partial(add, 3); add3(2) === 5;
93. const request = (defaults, options) => { options = Object.assign({}, defaults, options); return fetch(options.url, options) .then(resp => resp.json()); }; const customRequest = partial(request, { headers: { 'X-Custom': 'mykey' } }); const usersPromise = customRequest({ url: '/users' }); const tasksPromise = customRequest({ url: '/tasks' });
94. const request = (defaults, options) => { options = Object.assign({}, defaults, options); return fetch(options.url, options) .then(resp => resp.json()); }; const customRequest = partial(request, { headers: { 'X-Custom': 'mykey' } }); const usersPromise = customRequest({ url: '/users' }); const tasksPromise = customRequest({ url: '/tasks' });
95. const partialFromBind = (fn, ...args) => { return fn.bind(null, ...args); }; const partial = (fn, ...args) => { return (...otherArgs) => { return fn(...args, ...otherArgs) }; };
96. const partialFromBind = (fn, ...args) => { return fn.bind(null, ...args); }; const partial = (fn, ...args) => { return (...otherArgs) => { return fn(...args, ...otherArgs) }; };
97. const partialFromBind = (fn, ...args) => { return fn.bind(null, ...args); }; const partial = (fn, ...args) => { return (...otherArgs) => { return fn(...args, ...otherArgs) }; };
98. const partialFromBind = (fn, ...args) => { return fn.bind(null, ...args); }; const partial = (fn, ...args) => { return (...otherArgs) => { return fn(...args, ...otherArgs) }; };
99. const partialFromBind = (fn, ...args) => { return fn.bind(null, ...args); }; const partial = (fn, ...args) => { return (...otherArgs) => { return fn(...args, ...otherArgs) }; };
100. const partialFromBind = (fn, ...args) => { return fn.bind(null, ...args); }; const partial = (fn, ...args) => { return (...otherArgs) => { return fn(...args, ...otherArgs) }; };
101. CURRYING
102. const add3 = add(3); add3(2) === 5; const customRequest = request({ headers: { 'X-Custom': 'mykey' } }); const usersPromise = customRequest({ url: '/users' }); const tasksPromise = customRequest({ url: '/tasks' });
103. const add3 = add(3); add3(2) === 5; const customRequest = request({ headers: { 'X-Custom': 'mykey' } }); const usersPromise = customRequest({ url: '/users' }); const tasksPromise = customRequest({ url: '/tasks' });
104. const add = x => y => x + y; function add(x) { return function(y) { return x + y; }; }
105. const add = x => y => x + y; function add(x) { return function(y) { return x + y; }; }
106. const add = x => y => x + y; function add(x) { return function(y) { return x + y; }; }
107. const request = defaults => options => { options = Object.assign( {}, defaults, options ); return fetch(options.url, options) .then(resp => resp.json()); };
108. const request = defaults => options => { options = Object.assign( {}, defaults, options ); return fetch(options.url, options) .then(resp => resp.json()); };
109. PIECING IT TOGETHER
110. const map = fn => array => array.map(fn); const multiply = x => y => x * y; const pluck = key => object => object[key]; const discount = multiply(0.98); const tax = multiply(1.0925); const customRequest = request({ headers: { 'X-Custom': 'mykey' } }); customRequest({ url: '/cart/items' }) .then(map(pluck('price'))) .then(map(discount)) .then(map(tax));
111. const map = fn => array => array.map(fn); const multiply = x => y => x * y; const pluck = key => object => object[key]; const discount = multiply(0.98); const tax = multiply(1.0925); const customRequest = request({ headers: { 'X-Custom': 'mykey' } }); customRequest({ url: '/cart/items' }) .then(map(pluck('price'))) .then(map(discount)) .then(map(tax));
112. const map = fn => array => array.map(fn); const multiply = x => y => x * y; const pluck = key => object => object[key]; const discount = multiply(0.98); const tax = multiply(1.0925); const customRequest = request({ headers: { 'X-Custom': 'mykey' } }); customRequest({ url: '/cart/items' }) .then(map(pluck('price'))) .then(map(discount)) .then(map(tax));
113. const map = fn => array => array.map(fn); const multiply = x => y => x * y; const pluck = key => object => object[key]; const discount = multiply(0.98); const tax = multiply(1.0925); const customRequest = request({ headers: { 'X-Custom': 'mykey' } }); customRequest({ url: '/cart/items' }) .then(map(pluck('price'))) .then(map(discount)) .then(map(tax));
114. const map = fn => array => array.map(fn); const multiply = x => y => x * y; const pluck = key => object => object[key]; const discount = multiply(0.98); const tax = multiply(1.0925); const customRequest = request({ headers: { 'X-Custom': 'mykey' } }); customRequest({ url: '/cart/items' }) .then(map(pluck('price'))) .then(map(discount)) .then(map(tax));
115. const map = fn => array => array.map(fn); const multiply = x => y => x * y; const pluck = key => object => object[key]; const discount = multiply(0.98); const tax = multiply(1.0925); const customRequest = request({ headers: { 'X-Custom': 'mykey' } }); customRequest({ url: '/cart/items' }) .then(map(pluck('price'))) .then(map(discount)) .then(map(tax));
116. const map = fn => array => array.map(fn); const multiply = x => y => x * y; const pluck = key => object => object[key]; const discount = multiply(0.98); const tax = multiply(1.0925); const customRequest = request({ headers: { 'X-Custom': 'mykey' } }); customRequest({ url: '/cart/items' }) .then(map(pluck('price'))) .then(map(discount)) .then(map(tax));
117. customRequest({ url: '/cart/items' }) .then(map(pluck('price'))) .then(map(discount)) .then(map(tax)); [ { price: 5 }, { price: 10 }, { price: 3 }, ]
118. [ { price: 5 }, { price: 10 }, { price: 3 }, ] map(pluck('price')) [ 5, 10, 3, ] item.price
119. [ 5, 10, 3, ] map(discount) [ 4.9, 9.8, 2.94, ] price * 0.98
120. [ 5.35, 10.71, 3.21, ] map(tax) [ 4.9, 9.8, 2.94, ] price * 1.0925
121. COMPOSING CLOSURES
123. const processWord = compose(hyphenate, reverse, toUpperCase); const words = [ 'hello', 'functional', 'programming' ]; const newWords = words.map(processWord); console.log(newWords); // ['OL-LEH, 'LANOI-TCNUF', 'GNIMM-ARGORP']
124. const processWord = compose(hyphenate, reverse, toUpperCase); const words = [ 'hello', 'functional', 'programming' ]; const newWords = words.map(processWord); console.log(newWords); // ['OL-LEH, 'LANOI-TCNUF', 'GNIMM-ARGORP']
125. const processWord = compose(hyphenate, reverse, toUpperCase); const processWordExplicit = (word) => { return hyphenate(reverse(toUpperCase(word))); };
126. const compose = (...fns) => arg => ( fns.reduceRight( (result, fn) => fn(result), arg ) );
127. const compose = (...fns) => arg => ( fns.reduceRight( (result, fn) => fn(result), arg ) );
128. const compose = (...fns) => arg => ( fns.reduceRight( (result, fn) => fn(result), arg ) );
129. const compose = (...fns) => arg => ( fns.reduceRight( (result, fn) => fn(result), arg ) );
130. const compose = (...fns) => arg => ( fns.reduceRight( (result, fn) => fn(result), arg ) );
131. const compose = (...fns) => arg => ( fns.reduceRight( (result, fn) => fn(result), arg ) );
132. const compose = (...fns) => arg => ( fns.reduceRight( (result, fn) => fn(result), arg ) ); fns = [hyphenate, reverse, toUpperCase] arg = result = 'hello'
133. const compose = (...fns) => arg => ( fns.reduceRight( (result, fn) => fn(result), arg ) ); fns = [hyphenate, reverse] result = 'HELLO'
134. const compose = (...fns) => arg => ( fns.reduceRight( (result, fn) => fn(result), arg ) ); fns = [hyphenate] result = 'OLLEH'
135. const compose = (...fns) => arg => ( fns.reduceRight( (result, fn) => fn(result), arg ) ); fns = [] result = 'OL-LEH'
136. customRequest({ url: '/cart/items' }) .then(map(pluck('price'))) .then(map(discount)) .then(map(tax)); RETURNING TO PRICES EXAMPLE
137. customRequest({ url: '/cart/items' }) .then(map(pluck('price'))) .then(map(discount)) .then(map(tax)); Triple iteration RETURNING TO PRICES EXAMPLE
138. customRequest({ url: '/cart/items' }) .then(map( compose( tax, discount, pluck('price') ) )); Single iteration
139. RECURSION SOLVE A PROBLEM IN TERMS OF ITSELF
140. FACTORIAL
141. const factorial = (n) => { let result = 1; while (n > 1) { result *= n; n--; } return result; };
142. const factorial = (n) => { if (n < 2) { return 1; } return n * factorial(n - 1); };
143. const factorial = (n) => { if (n < 2) { return 1; } return n * factorial(n - 1); }; Recursive call
144. const factorial = (n) => { if (n < 2) { return 1; } return n * factorial(n - 1); }; Base case
145. factorial(4);
146. factorial(4); 4 * factorial(3);
147. factorial(4); 4 * factorial(3); 4 * 3 * factorial(2);
148. factorial(4); 4 * factorial(3); 4 * 3 * factorial(2); 4 * 3 * 2 * factorial(1);
149. factorial(4); 4 * factorial(3); 4 * 3 * factorial(2); 4 * 3 * 2 * factorial(1); 4 * 3 * 2 * 1;
150. factorial(4); 4 * factorial(3); 4 * 3 * factorial(2); 4 * 3 * 2 * factorial(1); 4 * 3 * 2 * 1; 4 * 3 * 2;
151. factorial(4); 4 * factorial(3); 4 * 3 * factorial(2); 4 * 3 * 2 * factorial(1); 4 * 3 * 2 * 1; 4 * 3 * 2; 4 * 6;
152. factorial(4); 4 * factorial(3); 4 * 3 * factorial(2); 4 * 3 * 2 * factorial(1); 4 * 3 * 2 * 1; 4 * 3 * 2; 4 * 6; 24;
153. STEPS Find the recurrence
 (n × n-1 × n-2 × … 1)
 Find the base case
 (n < 2)
154. PERFORMANCE RECURSION
155. const value = factorial(100000); console.log(value); // ??? WHAT IS THE RESULT?
156. const value = factorial(100000); console.log(value); // ??? WHAT IS THE RESULT? RangeError: Maximum call stack size exceeded
157. factorial(4); 4 * factorial(3); 4 * 3 * factorial(2); 4 * 3 * 2 * factorial(1); 4 * 3 * 2 * 1; 4 * 3 * 2; 4 * 6; 24; <main> Call Stack
158. factorial(4); 4 * factorial(3); 4 * 3 * factorial(2); 4 * 3 * 2 * factorial(1); 4 * 3 * 2 * 1; 4 * 3 * 2; 4 * 6; 24; <main> factorial(4) Call Stack
159. factorial(4); 4 * factorial(3); 4 * 3 * factorial(2); 4 * 3 * 2 * factorial(1); 4 * 3 * 2 * 1; 4 * 3 * 2; 4 * 6; 24; <main> factorial(4) factorial(3) Call Stack
160. factorial(4); 4 * factorial(3); 4 * 3 * factorial(2); 4 * 3 * 2 * factorial(1); 4 * 3 * 2 * 1; 4 * 3 * 2; 4 * 6; 24; <main> factorial(4) factorial(3) factorial(2) Call Stack
161. factorial(4); 4 * factorial(3); 4 * 3 * factorial(2); 4 * 3 * 2 * factorial(1); 4 * 3 * 2 * 1; 4 * 3 * 2; 4 * 6; 24; <main> factorial(4) factorial(3) factorial(2) factorial(1) Call Stack
162. factorial(4); 4 * factorial(3); 4 * 3 * factorial(2); 4 * 3 * 2 * factorial(1); 4 * 3 * 2 * 1; 4 * 3 * 2; 4 * 6; 24; <main> factorial(4) factorial(3) factorial(2) Call Stack
163. factorial(4); 4 * factorial(3); 4 * 3 * factorial(2); 4 * 3 * 2 * factorial(1); 4 * 3 * 2 * 1; 4 * 3 * 2; 4 * 6; 24; <main> factorial(4) factorial(3) Call Stack
164. factorial(4); 4 * factorial(3); 4 * 3 * factorial(2); 4 * 3 * 2 * factorial(1); 4 * 3 * 2 * 1; 4 * 3 * 2; 4 * 6; 24; <main> factorial(4) Call Stack
165. factorial(4); 4 * factorial(3); 4 * 3 * factorial(2); 4 * 3 * 2 * factorial(1); 4 * 3 * 2 * 1; 4 * 3 * 2; 4 * 6; 24; <main> Call Stack
166. const value = factorial(100000); console.log(value); // ??? 100,000 calls = 100,000 stack frames 1 stack frame ≈ 48B Max stack usage ≈ 1MB 100,000 x 48 / 1024 / 1024 = 4.58MB > 1MB
167. IN ES2015! TAIL CALL OPTIMIZATION
168. const factorial = (n) => { if (n < 2) { return 1; } return n * factorial(n - 1); }; UNOPTIMIZABLE
169. const factorial = (n) => { if (n < 2) { return 1; } return n * factorial(n - 1); }; 1 UNOPTIMIZABLE
170. const factorial = (n) => { if (n < 2) { return 1; } return n * factorial(n - 1); }; 1 UNOPTIMIZABLE 2
171. const factorial = (n) => { if (n < 2) { return 1; } return n * factorial(n - 1); }; 1 UNOPTIMIZABLE 2 3
172. const factorial = (n, accum = 1) => { if (n < 2) { return accum; } return factorial(n - 1, n * accum); }; OPTIMIZABLE
173. const factorial = (n, accum = 1) => { if (n < 2) { return accum; } return factorial(n - 1, n * accum); }; OPTIMIZABLE
174. const factorial = (n, accum = 1) => { if (n < 2) { return accum; } return factorial(n - 1, n * accum); }; OPTIMIZABLE
175. const factorial = (n, accum = 1) => { if (n < 2) { return accum; } return factorial(n - 1, n * accum); }; OPTIMIZABLE
176. const factorial = (n, accum = 1) => { if (n < 2) { return accum; } return factorial(n - 1, n * accum); }; 1 OPTIMIZABLE
177. const factorial = (n, accum = 1) => { if (n < 2) { return accum; } return factorial(n - 1, n * accum); }; 1 2 OPTIMIZABLE
178. const factorial = (n, accum = 1) => { if (n < 2) { return accum; } return factorial(n - 1, n * accum); }; 1 2 3 OPTIMIZABLE
179. const value = factorial(100000); console.log(value); // Infinity
180. factorial(4 /*, 1 */); factorial(3, 4); factorial(2, 12); factorial(1, 24); 24; <main> Call Stack
181. factorial(4 /*, 1 */); factorial(3, 4); factorial(2, 12); factorial(1, 24); 24; <main> factorial(4, 1) Call Stack
182. factorial(4 /*, 1 */); factorial(3, 4); factorial(2, 12); factorial(1, 24); 24; <main> factorial(3, 4) Call Stack
183. factorial(4 /*, 1 */); factorial(3, 4); factorial(2, 12); factorial(1, 24); 24; <main> factorial(2, 12) Call Stack
184. factorial(4 /*, 1 */); factorial(3, 4); factorial(2, 12); factorial(1, 24); 24; <main> factorial(1, 24) Call Stack
185. factorial(4 /*, 1 */); factorial(3, 4); factorial(2, 12); factorial(1, 24); 24; <main> Call Stack
186. RECAP PREDICTABLE SAFE TRANSPARENT MODULAR
187. DEMO
188. RESOURCES
189. drboolean.gitbooks.io/mostly-adequate-guide Brian Lonsdorf
190. ES6/7/LATER babeljs.io
191. LANGUAGES Elm (elm-lang.org) Clojurescript (github.com/clojure/clojurescript) Purescript (purescript.org)
192. LIBRARIES Lodash (lodash.com) Ramda (ramdajs.com) Rx (reactivex.io) Bacon.js (baconjs.github.io) Immutable.js (facebook.github.io/immutable-js)
193. “MV*” React (facebook.github.io/react) Redux (redux.js.org)
194. THANKS! Jeremy Fairbank blog.jeremyfairbank.com @elpapapollo / jfairbank Code: github.com/jfairbank/fp-basics-in-es6 Slides: bit.ly/devnexus-fp-basics