Programação Funcional com ES6

Uma introdução a Programação Funcional, usando exemplos com ES6, para despertar o interesse através de motivações reais e claras do porquê do uso da mesma.

Transcript

21. var daysThisMonth = function() { var date = new Date(); var year = date.getFullYear(); var month = date.getMonth(); var start = new Date(year, month, 1); var end = new Date(year, month + 1, 1); return Math.round((end - start) / (1000 * 60 * 60 * 24)); };
22. /* Se invocar em Março */ daysThisMonth(); // 31 /* Se invocar em Abril */ daysThisMonth(); // 30
23. var daysInMonth = function(year, month) { var start = new Date(year, month - 1, 1); var end = new Date(year, month, 1); return Math.round((end - start) / (1000 * 60 * 60 * 24)); };
24. /* Se invocar em Março */ daysInMonth(2016, 3); // 31 daysInMonth(2016, 3); // 31 daysInMonth(2016, 3); // 31 /* Se invocar em Abril */ daysInMonth(2016, 4); // 30 daysInMonth(2016, 4); // 30
26. var counter = 0; var increment = function() { counter = counter + 1; return counter; };
27. increment(); // 1 increment(); // 2 increment(); // 3 console.log(counter); // 3
28. var counter = 0; var increment = function(counter) { return counter + 1; };
29. increment(counter); // 1 increment(counter); // 1 increment(counter); // 1 console.log(counter); // 0
31. var printSquares = function() { for (var i = 1; i <= 10; i++) { console.log(i*i); } };
32. var printSquares = function(n) { if (n > 0) { printSquares(n-1); console.log(n*n); } };
33. printSquares(100000); Uncaught RangeError: Maximum call stack size exceeded
36. •
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43. • • • • •
45. var add = function (x, y) { return x + y; };
46. let add = function (x, y) { return x + y; };
47. let add = function (x, y) { return x + y; }; add = 42;
48. const add = function (x, y) { return x + y; }; add = 42; // Uncaught SyntaxError: unknown: Line 5: "add" is read-only
49. const add = function (x, y) { return x + y; };
50. const add = (x, y) => { return x + y; };
51. const add = (x, y) => return x + y;
52. const add = (x, y) => x + y;
53. const add = (x, y) => x + y
54. var add = function (x, y) { return x + y; }; const add = (x, y) => x + y
56. const add = (x, y) => x + y const mult = (x, y) => x * y const calculate = (fn, x, y) => fn(x, y) calculate(add, 1, 2) // 3 calculate(mult, 1, 2) // 2
57. const students = [ {name: 'Anna', grade: 6}, {name: 'John', grade: 4}, {name: 'Maria', grade: 9} ] ['Anna', 'John', 'Maria']
58. const students = [{name: 'Anna', grade: 6}, {name: 'John', grade: 4}, {name: 'Maria', grade: 9}] const studentsByName = [] for (const student of students) studentsByName.push(student.name)
59. const students = [{name: 'Anna', grade: 6}, {name: 'John', grade: 4}, {name: 'Maria', grade: 9}] const studentsByName = students.map(student => student.name)
60. const students = [{name: 'Anna', grade: 6}, {name: 'John', grade: 4}, {name: 'Maria', grade: 9}] const byName = object => object.name const studentsByName = students.map(byName)
61. const students = [ {name: 'Anna', grade: 6}, {name: 'John', grade: 4}, {name: 'Maria', grade: 9} ] [{name: 'Maria', grade: 9}]
62. const students = [{name: 'Anna', grade: 6}, {name: 'John', grade: 4}, {name: 'Maria', grade: 9}] const approvedStudents = [] for (const student of students) if (student.grade >= 9) approvedStudents.push(student.name)
63. const students = [{name: 'Anna', grade: 6}, {name: 'John', grade: 4}, {name: 'Maria', grade: 9}] const isApproved = student => student.grade >= 9 const approvedStudents = students.filter(isApproved)
64. const students = [ {name: 'Anna', grade: 6}, {name: 'John', grade: 4}, {name: 'Maria', grade: 9} ] 19
65. const students = [{name: 'Anna', grade: 6}, {name: 'John', grade: 4}, {name: 'Maria', grade: 9}] let sum = 0 for (let student of students) sum += student.grade
66. const students = [{name: 'Anna', grade: 6}, {name: 'John', grade: 4}, {name: 'Maria', grade: 9}] const sum = students.reduce((acc, current) => { return acc + current.grade }, 0)
67. const students = [{name: 'Anna', grade: 6}, {name: 'John', grade: 4}, {name: 'Maria', grade: 9}] const sum = students.reduce((acc, current) => acc + current.grade, 0)
68. const toUpperCase = x => x.toUpperCase() const exclaim = x => `${x}!!!` const scream = compose(exclaim, toUpperCase) scream("stop") // STOP!!!
69. const compose = (f,g) => x => f(g(x)) const toUpperCase = x => x.toUpperCase() const exclaim = x => `${x}!` const scream = compose(exclaim, toUpperCase) scream("stop") // STOP!!!
70. add(1, 2) // 3 add(1)(2) // 3
71. const add = (x, y) => { return x + y }
72. const add = (x, y) => { return x + y } const add = (x) => { }
73. const add = (x, y) => { return x + y } const add = (x) => { return (y) => { } }
74. const add = (x, y) => { return x + y } const add = (x) => { return (y) => { return x + y } }
75. const add = (x) => { return (y) => { return x + y } } const add = x => y => x + y
76. const add = x => y => x + y const addFive = add(5) console.log(addFive) // function (y) { return x + y; } console.log(addFive(3)) // 8
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