Effective ES6

1. Effective ES6 @teppeis YAPC::Asia Tokyo 2015 Aug 21

2. Hello! • Teppei Sato, @teppeis • Cybozu, Inc. / kintone • This is my ﬁrst and last YAPC :)

3. I created

4. http://cybozushiki.cybozu.co.jp/articles/m000978.html

5. kintone.com

6. MUST BUY!

7. Today talk about: • Introduce ES6 features • Deprecated best-practice/patterns • What’s ES2016, ES2017… • How to use ES6 from now

8. Background

9. –Brendan Eich from Effective JavaScript “My solution to the challenging requirements and crazy-short schedule was to make JavaScript extremely malleable from the start.” https://www.ﬂickr.com/photos/jsconf/4587502948/

10. –Douglas Crockford 2001, http://www.crockford.com/javascript/javascript.html “JavaScript: The world’s most misunderstood programming language” https://www.ﬂickr.com/photos/charliebrewer/2897862701/

11. JavaScript has many pitfalls… • Prototype inheritance (No class) • new, this • Function scope (No block scope) • Global variables (No module system) • Hoisting • NaN, undeﬁned • typeof null • with, eval

12. Example: No Class function Person(name) { this.name = name; } Person.prototype.greet = function() { console.log("Hello, I'm " + this.name); }; var bob = new Person("Bob"); bob.greet(); // "Hello, I'm Bob" • Use Prototype to emulate Classes

13. If you miss "new", dangerous! function Person(name) { this.name = name; } // Oh! You forget `new` var bob = Person("Bob"); console.log(bob); // undefined // Global leak!!!!!!!!!! console.log(window.name); // "Bob"

14. We've made best-practices a.k.a. “work around”

15. Practice: Be sure to call with "new" function Person(name) { // check! if (this instanceof Person) { return new Person(name); } this.name = name; } // without `new` var bob = Person("Bob"); bob.greet(); // "Hello, I'm Bob"

16. ES6!

17. ECMAScript 6 • Published on June 17, 2015 • Formally "ECMAScript 2015" • 6 years! from ES5

18. ECMAScript 6 • Modern syntax ﬁxing pitfalls • Better support for large applications • No (or few) breaking changes

19. For example: ES6 Classes

20. ES6 Classes: Simple! class Person { constructor(name) { this.name = name; } greet() { console.log("Hello, I'm " + this.name); } } var bob = new Person("Bob"); bob.greet(); // without `new` var bob = Person("Bob"); // Error!

21. Classes based on Prototype function Person(name) { this.name = name; } Person.prototype.greet = function() { console.log("Hello, I'm " + this.name); }; var bob = new Person("Bob"); bob.greet(); // "Hello, I'm Bob" OUT OF DATE!

22. Be sure to call with `new` function Person(name) { // check! if (this instanceof Person) { return new Person(name); } this.name = name; } // without `new` var bob = Person("Bob"); bob.greet(); // "Hello, I'm Bob" OUT OF DATE!

23. New ES6 features deprecates yesterday’s best-practices No more altJS! https://www.ﬂickr.com/photos/jorge-11/2765216505/

24. Can I use ES6 now?

25. ES6 compatibility table https://kangax.github.io/compat-table/es6/

26. You can use ES6 now! • Modern browsers and io.js (node.js) support   half of ES6 features. • Safari 9 (WebKit) will support many ES6 features soon. • Except for IE11…

27. Transpiler and polyﬁll • ES6 Transpiler:  source code converter from ES6 to ES5/ES3 • ES6 Polyﬁll:  library to provide ES6 built-in classes, functions and objects for ES5/ES3

28. Babel

29. Babel • The most compatible (71%) ES6 transpiler • Integrated with core-js (polyﬁll library) • Usage: • CLI: npm i -g babel • Browserify: babelify • REPL on the Web (Try it out!)

30. Babel REPL on the Web

31. ES6 features

32. ES6 features • New syntax • New built-in classes and objects • Improvement of existing classes

34. New syntax • Arrow Function • Classes • Modules • Block Scope (let/const) • Extended Object Literal • Default Params • Rest Params • Spread Operator • Destructuring • Iterator • Generator • Template Literal • Tail Call Optimization

35. Arrow Function

36. Prefer arrow function // ES5 old function var add = function(a, b) { return a + b; }; // ES6 arrow function! var add = (a, b) => { return a + b; }; var add = (a, b) => a + b; var square = n => n * n; // good for array filter chains [1, 2, 3, 4].filter(n => n % 2 === 0).map(n => n * n);

37. Assign “this” to “self” var john = { name: "John", helloLater: function() { // save `this` as `self` var self = this; setTimeout(function() { // `this` is not available. use `self`. console.log("Hello, I'm " + self.name); }, 1000); } } john.helloLater(); // "Hello, I'm John" after 1sec OUT OF DATE!

38. Arrow function don’t need "self" let john = { name: "John", helloLater: function() { // use arrow function setTimeout(() => { // `this` is available here! console.log("Hello, I'm " + this.name); }, 1000); } } john.helloLater(); // "Hello, I'm John" after 1sec

39. Classes

40. ES6 Classes class Person { constructor(name) { this.name = name; } greet() { console.log("Hello, I'm " + this.name); } } var bob = new Person("Bob"); bob.greet();

41. Classes based on Prototype function Person(name) { this.name = name; } Person.prototype.greet = function() { console.log("Hello, I'm " + this.name); }; var bob = new Person("Bob"); bob.greet(); // "Hello, I'm Bob" OUT OF DATE!

42. Handmade inheritance function // handmade function to extend function __extends(child, parent) { for (var key in parent) { if (Object.prototype.hasOwnProperty.call(parent, key)) { child[key] = parent[key]; } } function ctor() { this.constructor = child; } ctor.prototype = parent.prototype; child.prototype = new ctor(); child.__super__ = parent.prototype; return child; }; function Programmer(name, language) { Person.call(this, name); this.language = language; } __extends(Programmer, Person); OUT OF DATE!

43. ES6 Class inheritance class Programmer extends Person { constructor(name, language) { super(name); this.language = language; } greet() { super.greet(); console.log("I like " + this.language); } } var bob = new Programmer("Bob", "JavaScript"); bob.greet(); // "Hello, I'm Bob" // "I like JavaScript" • with "extends" and "super" • can extends built-in classes like "Error"

44. Modules

45. Module pattern // Global module var myModule = (function () { // Module object var module = {}, privateVariable = "Hello World"; function privateMethod() { // ... } module.publicProperty = "Foobar"; module.publicMethod = function () { console.log( privateVariable ); }; return module; })(); OUT OF DATE!

46. CommonJS Modules // import var foo = require('foo'); foo(); // export exports.bar = function() { console.log('bar'); } OUT OF DATE! • node.js/npm friendly • browserify/webpack to build for browser

47. ES6 Modules • run anywhere (browsers, node.js…) if ES6 available • easy to parse statically • strict mode by default in modules // export (./module.js) export var foo = "foo!"; export function bar() {} export class Baz { baz() {} } // import import {foo, bar, Baz} from "./module"; console.log(foo); // "foo!" bar(); new Baz();

48. Write “use strict;” • Strict mode is useful even in ES6. • In ES6 Module, always strict mode! • You don’t have write “use strict;” in ES6 modules. "use strict"; // Error! with (obj) {} // Error! var obj = {a: 1, a: 1}; OUT OF DATE!

49. Block Scope (let/const)

50. ES5 has only function scope function foo() { var num = 1; // ... too many statements if (true_condition) { // same scope! overwrite above `num`! var num = 2; // .. some process } console.log(num); // 2 !!! }

51. Weird hoisting（巻き上げ） var a = 'outer'; function bar() { console.log(a); var a = 'inner'; } bar(); // undefined !!!

52. Weird hoisting（巻き上げ） var a = 'outer'; function bar() { // hoisting! var a; console.log(a); a = 'inner'; } bar(); // undefined !!!

53. Place “var”s at the top of the scope • for function scope and hoisting function init() { // `var` once at the top of the scope! var i, cell, cells = document.getElementsByTagName('td'); for (i = 0; i < cells.length; i++) { cell = cells[i]; cell.addEventListener('click', function() { cell.style.backgroundColor = '#00F'; }, false); } } OUT OF DATE!

54. Use ES6 let or const anytime! • let and const create block scope • no hoisting • no more "var"! function foo() { let num = 1; // ... too many statements if (true_condition) { // different scope! let num = 2; } console.log(num); // 1 }

55. with for-loop • each iterate creates its own block scope for (let i = 0; i < 5; i++) { // new block scope is created for each iteration setTimeout(() => console.log(i), i * 100); } // display "1", "2", "3", "4", "5"

56. const • immutable value (not immutable object) • use like Java's ﬁnal const foo = 1; foo = 100; // Error! const foo = 1000; // Error! // properties are mutable const obj = {}; obj.foo = 1; // No error

57. Default Parameters

58. Incorrect default params function add(a, b) { // if "a" is 0, 1 is assigned to "a". a = a || 1; b = b || 2; return a + b; } add(0, 0); // 1 + 2 = 3 • Incorrect, but occur frequently

59. function add(a, b) { // correct, but awful.. if (a === undefined) { a = 1; } if (b === undefined) { b = 2; } return a + b; } add(0, 0); // 0 + 0 = 0 Handmade default params comparing to undeﬁned OUT OF DATE!

60. ES6 Default Parameters // default value for each param function add(a = 1, b = 2) { return a + b; } add(); // 1 + 2 = 3 add(0); // 0 + 2 = 2 add(undefined, 0); // 1 + 0 = 1 add(0, 0); // 0 + 0 = 0

61. Rest Parameters

62. Use "arguments" for variable-length arguments function foo(first, second) { console.log("first:", first); console.log("second:", second); // arguments is an ArrayLike, not an Array. var rest = Array.prototype.slice.call(arguments, 2); console.log("rest:", rest); } foo(1, 2, 3, 4, 5); // first: 1 // second: 2 // rest: [3, 4, 5] OUT OF DATE!

63. ES6 Rest Params instead of arguments • You don’t have to use `arguments` function foo(first, second, ...rest) { console.log("first:", first); console.log("second:", second); console.log("rest:", rest); } foo(1, 2, 3, 4, 5); // first: 1 // second: 2 // rest: [3, 4, 5]

64. Destructuring

65. Destructuring assignment • Array assignment let match = /(d{4})(d{2})(d{2})/.exec("20151231"); // match: [2015151231, 2015, 12, 31] let [, year, month, day] = match; console.log(year, month, day); // 2015 12 31 // Swapping [x, y] = [y, x]

66. Destructuring assignment • Object assignment let {name: a, age: b} = {name: "Bob", age: 20}; console.log(a, b); // "Bob" 20 // shorthand let {name, age} = {name: "Bob", age: 20}; console.log(name, age); // "Bob" 20

67. Destructuring assignment • Function params like "named-params" • Options object param function draw(x, y, {width = 320, height = 160} = {}) { // do the task } size(0, 0); size(0, 0, {}); size(0, 0, {width: 1}); size(0, 0, {height: 2}); size(0, 0, {width: 1, height: 2});

68. Handmade Options object handlingOUT OF DATE! function draw(x, x, options) { if (options.width === undefined) { options.width = 320; } if (options.height === undefined) { options.height = 320; } // do the task }

69. Template Literal

70. Concat with "+" or String#join() // concat with variables var name = 'Bob'; var str = "Hello, I'm " + name + "."; // create multiple lines var multi = ["line1", "line2", "line3"].join("n"); OUT OF DATE!

71. Template Literal // interpolation var name = 'Bob'; var str = `Hello, I'm ${name}.`; // multiple lines var multi = `line1 line2 line3`; • back-quoted string

72. Extended Object Literal

73. Extended object literal for shorthand let foo = 1; let bar = 2; // shorthand let obj = {foo, bar}; // same as: {foo: foo, bar: bar}; let prefix = 'foo'; let obj = { // computed property [prefix + 'abc']: 1, // method definition without "function" keyword foo() { console.log('foo!'); } };

74. and… • Iterator • Spread Operator • Generator • Tail Call Optimization 78

76. New built-in classes and objects • Promise • Map • Set • WeakMap/WeakSet • TypedArray • Symbol • Proxy/Reﬂect

77. Promise

78. Callback args for async API function asyncTask(a, b, callback) { // ...some async task if (error) { callback(error); } else { callback(null, result); } } asyncTask(1, 2, function(error, result) { if (error) { // ...error handling } console.log(result); }); OUT OF DATE!

79. Callback args for async API asyncTask1(function(error, result) { if (error) { // ...error handling } asyncTask2(function(error, result) { if (error) { // ...error handling } asyncTask3(function(error, result) { if (error) { // ...error handling } }); }); }); OUT OF DATE!

80. ES6 Promise function asyncTask(a, b, callback) { // ...some async task return new Promise((resolve, reject) => { if (error) { reject(error); } else { resolve(result); } }); } asyncTask(1, 2).then(result => { console.log(result); }).catch(error => { // ...error handling });

81. ES6 Promise // series asyncTask1().then(result => { return asyncTask2(); }).then(result => { return asyncTask3(); }).catch(error => { // ...error handling });

82. ES6 Promise // parallel Promise.all([ asyncTask1(), asyncTask2(), asyncTask3() ]).then(results => { console.log(results[0]); // result of asyncTask1 });

83. Map/Set

84. Use Object as a dictionary // some keys are dangerous var obj = {}; var key = "toString"; obj[key] = "value1"; String(obj); // TypeError: can't convert obj to string OUT OF DATE! • some special keys are dangerous

85. Use Object as a dictionary // cannot use object as a key var key1 = {name: "key1"}; var key2 = {name: "key2"}; obj[key1] = "value1"; obj[key2] = "value2"; console.log(obj[key1]); // "value2" console.log(Object.keys(obj)); // ["[object Object]"] OUT OF DATE! • cannot use an object as a key

86. ES6 Map // no dangerous keys let map = new Map(); map.set("toString", "value1"); map.get("toString"); // "value1" String(map); // "[object Map]" // object as a key let key1 = {}; let key2 = {}; let m = new Map(); m.set(key1, "v1"); m.set(key2, "v2"); m.get(key1); // "v1"

87. ES6 Set let set = new Set(); set.add("value1"); console.log(set.size); // 1 // unique set.add("value1"); console.log(set.size); // 1 • not easy to implement Set in ES5

88. and… • WeakMap/WeakSet • TypedArray • Symbol • Proxy/Reﬂect

90. Improvement of existing classes • String • RegExp • Array • Object • Math • Number

91. Object

92. Object.assign var target = {a: 1, b: 2}; var s1 = {b: 3, c: 4}; var s2 = {c: 5, d: 6}; var ret = Object.assign(target, s1, s2); console.log(target); // {a: 1, b: 3, c: 5, d: 6} • no more $.extend() !

93. String

94. Unicode surrogate pair support • 野家 valid "𠮷野家".codePointAt(0).toString(16); // "20BB7" String.fromCodePoint(0x20BB7); // "𠮷"

95. New pitfalls

96. What's happen? if (a => 1) { // ... }

97. Oh! Arrow function! // expected if (a >= 1) { } // arrow function! confusing.. if (a => 1) { } // clear if ((a) => 1) { }

98. ESLint

99. ES.next = ES2016?

100. The TC39 Process: Annual • TC39 committee approves acceptance for each stage. Stage 0: Strawman (idea) Stage 1: Proposal (problem, solution and demo/polyﬁll) Stage 2: Draft (initial spec) Stage 3: Candidate (review and feedback) Stage 4: Finished (two implementations at least) • Stage 4 features are published as ES201X  on July every year.

101. Stage 3: Candidate

102. Exponentiation Operator // x ** y let squared = 2 ** 2; // same as: 2 * 2 let cubed = 2 ** 3; // same as: 2 * 2 * 2 // x **= y let a = 2; a **= 2; // same as: a = a * a;

103. Array.prototype.includes(str, pos) [1, 2, 3].includes(2); // true [1, 2, 3].includes(4); // false [1, 2, NaN].includes(NaN); // true ["a", "b", "c"].includes("a", 0); // true ["a", "b", "c"].includes("a", 1); // false

104. Stage 2: Draft

105. Object.observe(obj, observer) let records; function observer(recs) { records = recs; } let obj = {id: 1}; Object.observe(obj, observer); obj.a = 'b'; obj.id++; Object.deliverChangeRecords(observer); assertChangesAre(records, [ {object: obj, type: 'add', name: 'a'}, {object: obj, type: 'update', name: 'id', oldValue: 1} ]);

106. Async/await async function chainAnimationsAsync(elem, animations) { let ret = null; try { for (let anim of animations) { ret = await anim(elem); } } catch(e) { /* ignore */ } return ret; }

107. SIMD let a = SIMD.Float32x4(1.0, 2.0, 3.0, 4.0); let b = SIMD.Float32x4(5.0, 10.0, 15.0, 20.0); let c = SIMD.Float32x4.add(a,b); // c: (6.0, 12.0, 18.0, 24.0) • Single Instruction Multiple Data • Vector data calculation

108. How can I get along with ES6 and ES.next?

109. May the Babel be with you! • It's too far for all browsers to support ES6. • IE11 will live until Jun 10, 2023… • You will be able to stop transpiling features that browsers support natively. • Also ES201X features are available via Babel.

110. Design your policy: Which ES6 features do you use? • Which browsers/node.js do you support? • If you need IE8 (ES3), it's not easy to use ES6… • Which feature is effective for your project? • Is the feature easy to transpile/polyﬁll?

111. Easy to transpile/polyﬁll? • No problem Arrow function, let/const, Extended Object literal, Classes  Extended function params, Template literal, Map/Set, Promise… • Be careful/Partial Module, Generator, Symbol • Hard/Impossible WeakMap/Set, Proxy, Reﬂect, Tail Call Optimization

112. Customize Babel conﬁg • Specify TC39 Stage (default: Stage 2) • Specify your blacklist features // .babelrc { "stage": 3, "blacklist": [ "es6.tailCall", "regenerator" ] }

113. Conclusion

114. Conclusion • ES6 is awesome! • Some best-practices are deprecated. • Try ES6 with Babel from now!

115. MUST BUY!

116. Thanks!

Effective ES6

teppeis

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