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DevNexus 2017: Functional Programming Basics in ES6
Jeremy Fairbank
February 23, 2017
Programming
4
130
DevNexus 2017: Functional Programming Basics in ES6
Jeremy Fairbank
February 23, 2017
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Transcript
FUNCTIONAL PROGRAMMING Jeremy Fairbank blog.jeremyfairbank.com @elpapapollo / jfairbank BASICS IN
ES6
sigient.com
None
¯\_(ϑ)_/¯ WHAT IS FUNCTIONAL PROGRAMMING?
¯\_(ϑ)_/¯ WHY FUNCTIONAL PROGRAMMING?
None
Domain to Range
None
None
Domain Range
CALCULUS
PRINCIPLES
PURE & DECLARATIVE PREDICTABLE
IMMUTABLE STATE SAFE
FIRST CLASS STATE TRANSPARENT
COMPOSABLE FIRST CLASS CLOSURES MODULAR
ES2015 (ES6)
let age = 10; age = 11; const name =
'Tucker'; name = 'Sally'; All good Syntax error
const add = (x, y) => { return x +
y; }; const identity = x => x;
const add = (x, y) => { return x +
y; }; const identity = x => x;
const add = (x, y) => { return x +
y; }; const identity = x => x;
const add = (x, y) => { return x +
y; }; const identity = x => x;
const add = (x, y) => { return x +
y; }; const identity = x => x;
const add = (x, y) => { return x +
y; }; const identity = x => x;
const array = (...elements) => { return elements; }; array(1,
2, 3); // [1, 2, 3]
const array = (...elements) => { return elements; }; array(1,
2, 3); // [1, 2, 3]
const array = (...elements) => { return elements; }; array(1,
2, 3); // [1, 2, 3]
const array = (...elements) => { return elements; }; array(1,
2, 3); // [1, 2, 3]
const log = (...args) => { console.log(...args); }; log('Hello', 'DevNexus');
// Hello DevNexus
const log = (...args) => { console.log(...args); }; log('Hello', 'DevNexus');
// Hello DevNexus
const langs = [ 'JavaScript', 'Elm', 'Haskell', ]; const [js,
...rest] = langs; js === 'JavaScript'; rest[0] === 'Elm'; rest[1] === 'Haskell';
const langs = [ 'JavaScript', 'Elm', 'Haskell', ]; const [js,
...rest] = langs; js === 'JavaScript'; rest[0] === 'Elm'; rest[1] === 'Haskell';
const langs = [ 'JavaScript', 'Elm', 'Haskell', ]; const [js,
...rest] = langs; js === 'JavaScript'; rest[0] === 'Elm'; rest[1] === 'Haskell';
const langs = [ 'JavaScript', 'Elm', 'Haskell', ]; const [js,
...rest] = langs; js === 'JavaScript'; rest[0] === 'Elm'; rest[1] === 'Haskell';
const head = ([x]) => x; head([1, 2, 3]) ===
1;
const head = ([x]) => x; head([1, 2, 3]) ===
1;
const head = ([x]) => x; head([1, 2, 3]) ===
1;
const greet = (name, greeting = 'Hi') => { console.log(greeting,
name); }; greet('DevNexus', 'Hello'); // Hello DevNexus greet('Atlanta'); // Hi Atlanta
const greet = (name, greeting = 'Hi') => { console.log(greeting,
name); }; greet('DevNexus', 'Hello'); // Hello DevNexus greet('Atlanta'); // Hi Atlanta
const greet = (name, greeting = 'Hi') => { console.log(greeting,
name); }; greet('DevNexus', 'Hello'); // Hello DevNexus greet('Atlanta'); // Hi Atlanta
const greet = (name, greeting = 'Hi') => { console.log(greeting,
name); }; greet('DevNexus', 'Hello'); // Hello DevNexus greet('Atlanta'); // Hi Atlanta
Object.assign( {}, { hello: 'Atlanta' }, { hi: 'DevNexus' }
); // { // hello: 'Atlanta', // hi: 'DevNexus' // }
Object.assign( {}, { hello: 'Atlanta' }, { hi: 'DevNexus' }
); // { // hello: 'Atlanta', // hi: 'DevNexus' // }
Object.assign( {}, { hello: 'Atlanta' }, { hi: 'DevNexus' }
); // { // hello: 'Atlanta', // hi: 'DevNexus' // }
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; };
PURE
const add = (x, y) => x + y; add(2,
3) === 5; add(2, 3) === 5; add(2, 3) === 5;
const add = (x, y) => x + y; add(2,
3) === 5; add(2, 3) === 5; add(2, 3) === 5; Referentially transparent
× let name = 'Jeremy'; const getName = () =>
name; const setName = (newName) => { name = newName; }; const printUpperName = () => { console.log(name.toUpperCase()); };
× let name = 'Jeremy'; const getName = () =>
name; const setName = (newName) => { name = newName; }; const printUpperName = () => { console.log(name.toUpperCase()); };
× let name = 'Jeremy'; const getName = () =>
name; const setName = (newName) => { name = newName; }; const printUpperName = () => { console.log(name.toUpperCase()); };
× let name = 'Jeremy'; const getName = () =>
name; const setName = (newName) => { name = newName; }; const printUpperName = () => { console.log(name.toUpperCase()); };
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'); }); }); ×
HIDDEN STATE IS UNCERTAIN STATE
const upperName = (name) => name.toUpperCase(); describe('api', () => {
it('returns an uppercase name', () => { expect(upperName('Jeremy')).to.equal('JEREMY'); expect(upperName('Jet')).to.equal('JET'); }); }); ✓
HOW TO ACHIEVE THE RESULT IMPERATIVE
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]
DECLARE WHAT THE DESIRED RESULT IS DECLARATIVE
function doubleNumbers(numbers) { return numbers.map(n => n * 2); }
doubleNumbers([1, 2, 3]); // [2, 4, 6]
function doubleNumbers(numbers) { return numbers.map(n => n * 2); }
doubleNumbers([1, 2, 3]); // [2, 4, 6]
1 2 3 numbers.map(n => n * 2) 2 4
6 Domain Range
CREATE STATE, DON’T MUTATE IT IMMUTABLE
const hobbies = [ 'programming', 'reading', 'music', ]; const firstTwo
= hobbies.splice(0, 2); console.log(firstTwo); // ['programming', 'reading'] console.log(hobbies); // ['music']
const hobbies = [ 'programming', 'reading', 'music', ]; const firstTwo
= hobbies.splice(0, 2); console.log(firstTwo); // ['programming', 'reading'] console.log(hobbies); // ['music'] Slight typo + mutability
Object.freeze Immutable.js
const hobbies = Object.freeze([ 'programming', 'reading', 'music', ]); const firstTwo
= hobbies.splice(0, 2); // TypeError
const hobbies = Object.freeze([ 'programming', 'reading', 'music', ]); const firstTwo
= hobbies.splice(0, 2); // TypeError
FREE YOUR STATE
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] ×
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)
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)
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)
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)
PROS SAFETY FROM ACCIDENTAL MUTATION FREE UNDO/REDO LOGS — REDUX
EXPLICIT FLOW OF DATA CONCURRENCY SAFETY
CONS VERBOSE MORE OBJECT CREATION* MORE GARBAGE COLLECTION* MORE MEMORY
USAGE* *Alleviated with libs like Immutable.js
FIRST CLASS FUNCTIONS
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);
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);
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);
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);
ENCAPSULATION CLOSURES
const createAdder = (x) => { return (y) => x
+ y; }; const add3 = createAdder(3); add3(2) === 5; add3(3) === 6;
const createAdder = (x) => { return (y) => x
+ y; }; const add3 = createAdder(3); add3(2) === 5; add3(3) === 6;
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' } });
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
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' });
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' });
FOUNDATION FOR HIGHER ORDER PATTERNS FIRST CLASS CLOSURES
PARTIAL APPLICATION
const createAdder = (x) => { return (y) => x
+ y; }; const createRequester = (options) => { return (otherOptions) => { return request(Object.assign( {}, options, otherOptions )); }; }; RECALL
const add = (x, y) => x + y; const
add3 = partial(add, 3); add3(2) === 5;
const add = (x, y) => x + y; const
add3 = partial(add, 3); add3(2) === 5;
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' });
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' });
const partialFromBind = (fn, ...args) => { return fn.bind(null, ...args);
}; const partial = (fn, ...args) => { return (...otherArgs) => { return fn(...args, ...otherArgs) }; };
const partialFromBind = (fn, ...args) => { return fn.bind(null, ...args);
}; const partial = (fn, ...args) => { return (...otherArgs) => { return fn(...args, ...otherArgs) }; };
const partialFromBind = (fn, ...args) => { return fn.bind(null, ...args);
}; const partial = (fn, ...args) => { return (...otherArgs) => { return fn(...args, ...otherArgs) }; };
const partialFromBind = (fn, ...args) => { return fn.bind(null, ...args);
}; const partial = (fn, ...args) => { return (...otherArgs) => { return fn(...args, ...otherArgs) }; };
const partialFromBind = (fn, ...args) => { return fn.bind(null, ...args);
}; const partial = (fn, ...args) => { return (...otherArgs) => { return fn(...args, ...otherArgs) }; };
const partialFromBind = (fn, ...args) => { return fn.bind(null, ...args);
}; const partial = (fn, ...args) => { return (...otherArgs) => { return fn(...args, ...otherArgs) }; };
CURRYING
const add3 = add(3); add3(2) === 5; const customRequest =
request({ headers: { 'X-Custom': 'mykey' } }); const usersPromise = customRequest({ url: '/users' }); const tasksPromise = customRequest({ url: '/tasks' });
const add3 = add(3); add3(2) === 5; const customRequest =
request({ headers: { 'X-Custom': 'mykey' } }); const usersPromise = customRequest({ url: '/users' }); const tasksPromise = customRequest({ url: '/tasks' });
const add = x => y => x + y;
function add(x) { return function(y) { return x + y; }; }
const add = x => y => x + y;
function add(x) { return function(y) { return x + y; }; }
const add = x => y => x + y;
function add(x) { return function(y) { return x + y; }; }
const request = defaults => options => { options =
Object.assign( {}, defaults, options ); return fetch(options.url, options) .then(resp => resp.json()); };
const request = defaults => options => { options =
Object.assign( {}, defaults, options ); return fetch(options.url, options) .then(resp => resp.json()); };
PIECING IT TOGETHER
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));
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));
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));
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));
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));
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));
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));
customRequest({ url: '/cart/items' }) .then(map(pluck('price'))) .then(map(discount)) .then(map(tax)); [ { price:
5 }, { price: 10 }, { price: 3 }, ]
[ { price: 5 }, { price: 10 }, {
price: 3 }, ] map(pluck('price')) [ 5, 10, 3, ] item.price
[ 5, 10, 3, ] map(discount) [ 4.9, 9.8, 2.94,
] price * 0.98
[ 5.35, 10.71, 3.21, ] map(tax) [ 4.9, 9.8, 2.94,
] price * 1.0925
COMPOSING CLOSURES
None
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']
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']
const processWord = compose(hyphenate, reverse, toUpperCase); const processWordExplicit = (word)
=> { return hyphenate(reverse(toUpperCase(word))); };
const compose = (...fns) => arg => ( fns.reduceRight( (result,
fn) => fn(result), arg ) );
const compose = (...fns) => arg => ( fns.reduceRight( (result,
fn) => fn(result), arg ) );
const compose = (...fns) => arg => ( fns.reduceRight( (result,
fn) => fn(result), arg ) );
const compose = (...fns) => arg => ( fns.reduceRight( (result,
fn) => fn(result), arg ) );
const compose = (...fns) => arg => ( fns.reduceRight( (result,
fn) => fn(result), arg ) );
const compose = (...fns) => arg => ( fns.reduceRight( (result,
fn) => fn(result), arg ) );
const compose = (...fns) => arg => ( fns.reduceRight( (result,
fn) => fn(result), arg ) ); fns = [hyphenate, reverse, toUpperCase] arg = result = 'hello'
const compose = (...fns) => arg => ( fns.reduceRight( (result,
fn) => fn(result), arg ) ); fns = [hyphenate, reverse] result = 'HELLO'
const compose = (...fns) => arg => ( fns.reduceRight( (result,
fn) => fn(result), arg ) ); fns = [hyphenate] result = 'OLLEH'
const compose = (...fns) => arg => ( fns.reduceRight( (result,
fn) => fn(result), arg ) ); fns = [] result = 'OL-LEH'
customRequest({ url: '/cart/items' }) .then(map(pluck('price'))) .then(map(discount)) .then(map(tax)); RETURNING TO PRICES
EXAMPLE
customRequest({ url: '/cart/items' }) .then(map(pluck('price'))) .then(map(discount)) .then(map(tax)); Triple iteration RETURNING
TO PRICES EXAMPLE
customRequest({ url: '/cart/items' }) .then(map( compose( tax, discount, pluck('price') )
)); Single iteration
RECURSION SOLVE A PROBLEM IN TERMS OF ITSELF
FACTORIAL
const factorial = (n) => { let result = 1;
while (n > 1) { result *= n; n--; } return result; };
const factorial = (n) => { if (n < 2)
{ return 1; } return n * factorial(n - 1); };
const factorial = (n) => { if (n < 2)
{ return 1; } return n * factorial(n - 1); }; Recursive call
const factorial = (n) => { if (n < 2)
{ return 1; } return n * factorial(n - 1); }; Base case
factorial(4);
factorial(4); 4 * factorial(3);
factorial(4); 4 * factorial(3); 4 * 3 * factorial(2);
factorial(4); 4 * factorial(3); 4 * 3 * factorial(2); 4
* 3 * 2 * factorial(1);
factorial(4); 4 * factorial(3); 4 * 3 * factorial(2); 4
* 3 * 2 * factorial(1); 4 * 3 * 2 * 1;
factorial(4); 4 * factorial(3); 4 * 3 * factorial(2); 4
* 3 * 2 * factorial(1); 4 * 3 * 2 * 1; 4 * 3 * 2;
factorial(4); 4 * factorial(3); 4 * 3 * factorial(2); 4
* 3 * 2 * factorial(1); 4 * 3 * 2 * 1; 4 * 3 * 2; 4 * 6;
factorial(4); 4 * factorial(3); 4 * 3 * factorial(2); 4
* 3 * 2 * factorial(1); 4 * 3 * 2 * 1; 4 * 3 * 2; 4 * 6; 24;
STEPS Find the recurrence (n × n-1 × n-2 ×
… 1) Find the base case (n < 2)
PERFORMANCE RECURSION
const value = factorial(100000); console.log(value); // ??? WHAT IS THE
RESULT?
const value = factorial(100000); console.log(value); // ??? WHAT IS THE
RESULT? RangeError: Maximum call stack size exceeded
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
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
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
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
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
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
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
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
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
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
IN ES2015! TAIL CALL OPTIMIZATION
const factorial = (n) => { if (n < 2)
{ return 1; } return n * factorial(n - 1); }; UNOPTIMIZABLE
const factorial = (n) => { if (n < 2)
{ return 1; } return n * factorial(n - 1); }; 1 UNOPTIMIZABLE
const factorial = (n) => { if (n < 2)
{ return 1; } return n * factorial(n - 1); }; 1 UNOPTIMIZABLE 2
const factorial = (n) => { if (n < 2)
{ return 1; } return n * factorial(n - 1); }; 1 UNOPTIMIZABLE 2 3
const factorial = (n, accum = 1) => { if
(n < 2) { return accum; } return factorial(n - 1, n * accum); }; OPTIMIZABLE
const factorial = (n, accum = 1) => { if
(n < 2) { return accum; } return factorial(n - 1, n * accum); }; OPTIMIZABLE
const factorial = (n, accum = 1) => { if
(n < 2) { return accum; } return factorial(n - 1, n * accum); }; OPTIMIZABLE
const factorial = (n, accum = 1) => { if
(n < 2) { return accum; } return factorial(n - 1, n * accum); }; OPTIMIZABLE
const factorial = (n, accum = 1) => { if
(n < 2) { return accum; } return factorial(n - 1, n * accum); }; 1 OPTIMIZABLE
const factorial = (n, accum = 1) => { if
(n < 2) { return accum; } return factorial(n - 1, n * accum); }; 1 2 OPTIMIZABLE
const factorial = (n, accum = 1) => { if
(n < 2) { return accum; } return factorial(n - 1, n * accum); }; 1 2 3 OPTIMIZABLE
const value = factorial(100000); console.log(value); // Infinity
factorial(4 /*, 1 */); factorial(3, 4); factorial(2, 12); factorial(1, 24);
24; <main> Call Stack
factorial(4 /*, 1 */); factorial(3, 4); factorial(2, 12); factorial(1, 24);
24; <main> factorial(4, 1) Call Stack
factorial(4 /*, 1 */); factorial(3, 4); factorial(2, 12); factorial(1, 24);
24; <main> factorial(3, 4) Call Stack
factorial(4 /*, 1 */); factorial(3, 4); factorial(2, 12); factorial(1, 24);
24; <main> factorial(2, 12) Call Stack
factorial(4 /*, 1 */); factorial(3, 4); factorial(2, 12); factorial(1, 24);
24; <main> factorial(1, 24) Call Stack
factorial(4 /*, 1 */); factorial(3, 4); factorial(2, 12); factorial(1, 24);
24; <main> Call Stack
RECAP PREDICTABLE SAFE TRANSPARENT MODULAR
DEMO
RESOURCES
drboolean.gitbooks.io/mostly-adequate-guide Brian Lonsdorf
ES6/7/LATER babeljs.io
LANGUAGES Elm (elm-lang.org) Clojurescript (github.com/clojure/clojurescript) Purescript (purescript.org)
LIBRARIES Lodash (lodash.com) Ramda (ramdajs.com) Rx (reactivex.io) Bacon.js (baconjs.github.io) Immutable.js
(facebook.github.io/immutable-js)
“MV*” React (facebook.github.io/react) Redux (redux.js.org)
THANKS! Jeremy Fairbank blog.jeremyfairbank.com @elpapapollo / jfairbank Code: github.com/jfairbank/fp-basics-in-es6 Slides:
bit.ly/devnexus-fp-basics