บันทึก FunctionalPrograming

// ES6 [1, 2, 3].map(num => num * 2); // ES5 [1, 2, 3].map(function(num) { return num * 2; }); // ES6 app.get('/', (req, res) => { res.json({ message: 'Hello World' }); }); // ES5 app.get('/', function(req, res) { res.json({ message: 'Hello World' }); }); () => ‘Hello’ () => {} (แบบ code block) (num) => num * 2 (num1, num2) => {return num1 + num2;} (แบบ code block) () => ({ foo: ‘bar’ }) (return เป็น Object ให้ใช้ปีกกา) 

const f = x => x * 2 print(f(2)); //=========================== var materials = [ 'Hydrogen', 'Helium', 'Lithium', 'Beryllium' ]; //จัดให้ดูง่ายสำหรับผม const a = materials.map( function(material) { return material.length; } ); //เปลื่อน function เป็น => ไว้ด้านหลังแทน const b = materials.map( (material) => { return material.length; } ); // ลบ () ของ parameter ออก รวมถึง {},return ของ Function materials.map(material => material.length); //output [8, 6, 7, 9] //==================================== var simple = a => a > 15 ? 15 : a; print(simple(16)); print(simple(10)); // 15 10 const a = (a,b=10) => a*b print(a(2)); // 20 // ต้องใส่ () ด้วย ถ้าจะ Default const a = (a=5) => a print(a()); 

let add = (x,y) => x + y; add(2,3); //=> 5 let add = x => y => x + y; add(2)(3); let add = function (x) { return function (y) { return x + y; }; }; 

let numbers = [1, 2, 3, 4, 5, 6 ,7, 8, 9, 10]; let squaredEvens = []; for(let i = 0; i < numbers.length; i++) { let currentNumber = numbers[i]; if(currentNumber % 2 === 0) { squaredEvens.push(currentNumber * currentNumber) } } 

const numbers = [1, 2, 3, 4, 5, 6 ,7, 8, 9, 10]; const isEven = n => n % 2 === 0; const square = n => n * n; numbers.filter(isEven).map(square); 

function isEven(n) { return n % 2 === 0; } function square(n) { return n * n; } 

 const foo = [1,2,3]; const baz = foo.map(function bar (n) { return n + 1; }); 

 function ticker() { let count = 0; return () => count++; } let t = ticker(); t(); // 0 t(); // 1 t(); // 2 t(); // 3 

 // Original function makeAdder(a) { return b => a + b; } const addFive = makeAdder(5); const addTen = makeAdder(10); addFive(20); // 5 + 20 => 25 addTen(9); // 10 + 9 => 19 // Refactoring const makeAdder2 = a => b => a + b; const addfuck = makeAdder2(5) addfuck(20) 

 const makeSum = transFunc => (a, b) => transFunc(a) + transFunc(b); const sumSquared = makeSum(n => n * n); const sumCubed = makeSum(n => n * n * n); sumSquared(1, 2); // 1^2 + 2^2 => 5 sumCubed(1, 2); // 1^3 + 2^3 => 9 

console.log('Step 1'); funcSync(); console.log('Step 3'); function funcSync () { console.log('Step 2'); } 

 setTimeout(function(){ console.log('Step 1') }, 3000); console.log('Step 2') // ผลลัพท์ // Step 2 // Step 1 setTimeout(doSomeThing, 3000); function doSomeThing () { console.log('Hello') } 

 const myAsyncFunc = callback => callback(); myAsyncFunc(callbackFunc); function callbackFunc () { print('this is callback function') } 

// Original asyncFunc( function (str) { print('cb1 : ' + str); }, function (str) { print('cb2 : ' + str); } ); function asyncFunc (cb1, cb2) { cb1('A'); cb2('B'); } // Refactoring let asyncFunc = (cb1,cb2) => { cb1('A'); cb2('B'); } const f1 = str => print('cb1 : ' + str); const f2 = str => print('cb2 : ' + str); asyncFunc(f1,f2); 

// Original asyncFunc(cb, cb); function asyncFunc (cb1, cb2) { cb1('A'); cb2('B'); } function cb (str) { print('cb : ' + str); } // Refactoring const cb = str => print('cb : ' + str) let asyncFunc = (cb1,cb2) => { cb("A"); cb("B"); } asyncFunc(cb,cb); 

// Original asyncFunc(cb, cb); function asyncFunc (running, done) { for (var i = 0;i<10;i++) { running('i = ' + i); } done('done'); } function cb (str) { print(str); } // Refactoring let cb = str => print(str); let asyncFunc = (running, done) =>{ for (var i = 0;i<10;i++) { running('i = ' + i); } done('done'); } asyncFunc(cb, cb); 

var p = new Promise(function(resolve, reject) { let a = 5; if(a >= 5) { resolve(a); }else { reject(a); } }).then(function(a) { console.log(`result then : ${a}`); return a + 2; }).then(function(b) { console.log(`result then : ${b}`); }).catch(function(a) { console.log(`result catch : ${a}`); }); 

const resolveAfter2Seconds = x => { return new Promise( resolve => { setTimeout(() => { resolve(x); }, 2000); } ); } console.log(resolveAfter2Seconds(50)); async function add1(x) { const a = await resolveAfter2Seconds(20); const b = await resolveAfter2Seconds(30); return x + a + b; } console.log(add1(100)); add1(10).then(v => { console.log(v); // prints 60 after 4 seconds. }); async function add2(x) { const p_a = resolveAfter2Seconds(20); const p_b = resolveAfter2Seconds(30); return x + await p_a + await p_b; } add2(10).then(v => { console.log(v); // prints 60 after 2 seconds. }); 

const compose = function(f, g) { return function(x) { return f(g(x)) } } const compose = (f, g) => x => f(g(x)) 

function sanitize(str) { return str.trim().toLowerCase() } sanitize(' Hello My Name is Ham ') // 'hello my name is ham' 

const trim = s => s.trim() const toLowerCase = s => s.toLowerCase() function sanitize(str) { return toLowerCase(trim(str)) } sanitize(' Hello My Name is Ham ') // 'hello my name is ham' 

const compose = (f, g) => x => f(g(x)) const sanitize = compose(toLowerCase, trim) sanitize(' Hello My Name is Ham ') // 'hello my name is ham' 

const trim = s => s.trim() const toLowerCase = s => s.toLowerCase() const join = separator => arr => arr.join(separator) const split = separator => arr => arr.split(separator) const toSlug = compose( toLowerCase, join('-'), split(' '), trim, ) toSlug(' THIS is SluG ') // 'this-is-slug' 

const toSlug = pipe( trim, split(' '), join('-'), toLowerCase, ) toSlug(' THIS is SluG ') // 'this-is-slug'