Practical JavaScript Programming - Session 3/8

Practical JavaScript Programming
Session 3
Wilson Su

2
https://www.slideshare.net/sweekson/

Outline
3
Chapter 5.
● Function Definitions
● Function Parameters
● The Arguments Object
● What is ‘this’?
● Function Invocation
● Closures
Functions
Chapter 6.
Constructors And Prototypes
● Constructors
● Prototypes
● Inheritance
● Class

4
Wilson Su
Front-end Developer, HIE
● 6 years in web design
● Specialize in JavaScript /
CSS / HTML / OOP / Git
● Familiar with PHP / Design
Pattern
● Interested in UI & Ix Design
wilson_su@trend.com.tw

Parentheses
6
1. 5.toString(); // SyntaxError
2. (5).toString(); // '5'
3.
4. var good = { grade: 'A' }, bad = { grade: 'F' };
5. var score = 75;
6.
7. if (score > 60) {
8. good.grade; // 'A'
9. } else {
10. bad.grade;
11. }
12.
13. (score > 60 ? good : bad).grade; // 'A'

In JavaScript, functions are
first-class objects.
8

3 Ways To Define A Function
10
1. /* Function declarations */
2. function name ([param[, param[..., param]]]) {
3. [statements]
4. }
5.
6. /* Function expressions */
7. var name = function [name] ([param[, param[..., param]]]) {
8. [statements]
9. }
10.
11. /* Function Constructor */
12. var name = new Function([param[, param[..., param]],] body);

Function Declarations
11
1. function echo (value) { return value; }
2. typeof echo; // 'function'
3. echo.name; // 'echo'
4. echo.length; // 1
5. echo('ABC'); // 'ABC'
6.
7. function () {} // SyntaxError

Function Expressions
12
1. var multiply = function (x, y) {
2. return x * y;
3. };
4.
5. typeof multiply; // 'function'
6. multiply.name; // 'multiply'
7. multiply.length; // 2
8. multiply(2, 3); // 6
9.
10. (function (value) { return value; })
11. // function (value) { return value; }

Named Function Expressions
13
1. var calcalate = function calc (v1, v2) {
2. console.log(typeof calc); // 'function'
3. console.log(calcalate === calc); // true
4. return v1 + v2;
5. }
6.
7. typeof calcalate; // 'function'
8. calcalate.name; // 'calc'
9. calcalate.length; // 2
10. calcalate(2, 3); // 5
11. calc; // ?
1. var calcalate = function calc (v1, v2) {
2. console.log(typeof calc); // 'function'
3. console.log(calcalate === calc); // true
4. return v1 + v2;
5. }
6.
7. typeof calcalate; // 'function'
8. calcalate.name; // 'calc'
9. calcalate.length; // 2
10. calcalate(2, 3); // 5
11. calc; // ReferenceError

The Function() Constructor
14
1. var subtract = new Function('x', 'y', 'return x - y');
2.
3. typeof subtract; // 'function'
4. subtract.name; // 'anonymous'
5. subtract.length; // 2
6. subtract(18, 3); // 15

Functions created
with the Function constructor
always are created in
the global scope.
15

The Function() Constructor Create Functions In The Global Scope
16
1. var uppercaser = function (skill) {
2. return new Function('return skill.toUpperCase()');
3. };
4. var uppercase = uppercaser('html');
5. var skill = 'css';
6.
7. uppercase('js'); // ?
1. var uppercaser = function (skill) {
2. return new Function('return skill.toUpperCase()');
3. };
4. var uppercase = uppercaser('html');
5. var skill = 'css';
6.
7. uppercase('js'); // 'CSS'

Defining Object Methods
17
1. var dog = {
2. bark: function bowwow () {
3. console.log('Bowwow!');
4. }
5. };
6.
7. typeof dog.bark; // 'function'
8. dog.bark.name; // 'bowwow'
9. dog.bark.length; // 0
10. dog.bark(); // 'Bowwow!'

Defining Object Methods In A Shorter Syntax
18
1. var cat = {
2. meow () {
3. console.log('Meow~');
4. }
5. };
6.
7. typeof cat.meow; // 'function'
8. cat.meow.name; // 'meow'
9. cat.meow.length; // 0
10. cat.meow(); // 'Meow~'

Function Return
19
1. function noop () {}
2. function nothing () { return; }
3. function echo (value) { return value; }
4.
5. noop(true); // undefined
6. nothing('Hi'); // undefined
7. echo([10, 20]); // (2) [10, 20]

Function Hoisting
20
1. hello(); // 'Hello!'
2. aloha(); // ?
3.
4. function hello () {
5. return 'Hello!';
6. }
7.
8. var aloha = function () {
9. return 'Aloha!';
10. };
1. hello(); // 'Hello!'
2. aloha(); // TypeError
3.
4. function hello () {
5. return 'Hello!';
6. }
7.
8. var aloha = function () {
9. return 'Aloha!';
10. };

Nested Functions
21
1. function outer () {
2. function inner () {
3. return 'Inner';
4. }
5. return inner();
6. }
7.
8. outer(); // 'Inner';
9. inner(); // ?
3. return 'Inner';
4. }
5. return inner();
6. }
7.
8. outer(); // 'Inner';
9. inner(); // ReferenceError

Arrow Functions
22
1. var remove = (target, array) => {
2. var index = array.indexOf(target);
3. return index > -1 ? !!array.splice(index, 1) : false;
4. };
5. var concat = (list1, list2) => list1.concat(list2);
6. var numbers = [100, 200, 300];
7.
8. remove(200, numbers); // true
9. numbers; // (2) [100, 300]
10. concat(numbers, [500, 700]); // (4) [100, 300, 500, 700]
11. numbers; // ?
1. var remove = (target, array) => {
2. var index = array.indexOf(target);
3. return index > -1 ? !!array.splice(index, 1) : false;
4. };
5. var concat = (list1, list2) => list1.concat(list2);
6. var numbers = [100, 200, 300];
7.
8. remove(200, numbers); // true
9. numbers; // (2) [100, 300]
10. concat(numbers, [500, 700]); // (4) [100, 300, 500, 700]
11. numbers; // (2) [100, 300]

More Examples With Arrow Functions
23
1. var noop = () => {};
2. var book = title => ({ title });
3.
4. book('Zero to One'); // {title: 'Zero to One'}
5.
6. [{ id: 10 }, { id: 20 }, { id: 30 }].map(item => item.id);
7. // (3) [10, 20, 30]

Generator Functions
24
1. function* generator (x) {
2. yield x * 10;
3. yield x + 50;
4. }
5.
6. var iterator = generator(10);
7.
8. typeof generator; // 'function'
9. typeof iterator; // 'object'
10.
11. iterator.next(); // {value: 100, done: false}
12. iterator.next(); // {value: 60, done: false}
13. iterator.next(); // {value: undefined, done: true}

Parameter Defaults
26
1. function add (x, y) {
2. console.log(x); // 5
3. console.log(y); // undefined
4. console.log(x + y); // NaN
5. x = x || 0;
6. y = y || 0;
7. return x + y;
8. }
9.
10. add(5); // 5

Passed By Value / Passed By Reference
27
1. function update (string, object, array) {
2. string = 'aloha';
3. object.id = 2;
4. array = [];
5. }
6.
7. var string = 'hello', object = { id: 1 }, array = [10, 20];
8.
9. update(string, object, array);
10. console.log(string); // ?
11. console.log(object); // ?
12. console.log(array); // ?
3. object.id = 2;
4. array = [];
5. }
6.
8.
10. console.log(string); // 'hello'
11. console.log(object); // ?
3. object.id = 2;
4. array = [];
5. }
6.
8.
11. console.log(object); // {id: 2}
3. object.id = 2;
4. array = [];
5. }
6.
8.
11. console.log(object); // {id: 2}
12. console.log(array); // (2) [10, 20]

Default And Destructured Parameters
28
1. function fn1 (x = 0) {}
2.
3. function fn2 (x = y(), z = []) {}
4.
5. function fn3 (x, y = x, z = y + 1) {}
6.
7. function fn4 ({ multiplier = 3 }, [x, y, z = 5]) {}

Rest Parameters
29
1. function join (...args) {
2. return args.join(' ');
3. }
4. function sum (...[x, y, z]) {
5. return x + y + z;
6. }
7.
8. join('Ryan', 'likes', 'JS'); // 'Ryan likes JS'
9.
10. sum(1); // NaN
11. sum(1, 2, 3); // 6
12. sum(1, 2, 3, 4); // 6

The arguments Object
31
1. function fn () {
2. console.log(arguments);
3. }
4.
5. fn(10, 20); // (2) [10, 20]

The arguments object is not a
real array.
32

The arguments Object
33
1. function fn () {
2. console.log(arguments.length); // 2
3. console.log(arguments[0]); // 10
4. console.log(arguments[1]); // 20
5. console.log(typeof arguments); // 'object'
6. console.log(arguments instanceof Array); // false
7. }
8.
9. fn(10, 20);

From arguments To An Array
34
1. function toArray1 () {
2. return Array.prototype.slice.call(arguments, 0);
3. }
5. return [].slice.call(arguments, 0);
6. }
7.
8. toArray1(1, 2, 3); // (3) [1, 2, 3]
9. toArray1(1, 2, 3) instanceof Array; // true
10.
11. toArray2(4, 5, 6); // (3) [4, 5, 6]
12. toArray2(4, 5, 6) instanceof Array; // true

From arguments To An Array
35
2. return arguments.length === 1
3. ? [arguments[0]]
4. : Array.apply(null, arguments);
5. }
6.
7. /* ES6 */
9. return Array.from(arguments);
10. }

Destructuring
36
1. function fn () {
2. var args = [...arguments];
3. var [x, y, ...rest] = arguments;
4.
5. console.log(args); // (5) [10, 20, 30, 40, 50]
6. console.log(args instanceof Array); // true
7. console.log(x); // 10
8. console.log(y); // 20
9. console.log(rest); // (3) [30, 40, 50]
10. }
11.
12. fn(10, 20, 30, 40, 50);

Arrow funtions do not bind an
arguments object.
37

Arrow Funtions
38
1. var fn = () => arguments;
2. var calc = function () {
3. var fn = (multiple) => arguments[0] * multiple;
4. return fn(3);
5. };
6.
7. fn(); // ?
8. calc(8); // ?
4. return fn(3);
5. };
6.
7. fn(); // ReferenceError
8. calc(8); // ?
4. return fn(3);
5. };
6.
7. fn(); // ReferenceError
8. calc(8); // 24

Global Context
40
1. /* In a browser */
2. this; // Window { … }
3. this === window; // true
4.
5. /* In Node */
6. this; // {}
7. this === module.exports; // true

Function Context
41
1. /* In a browser */
2. var that = function () { return this; };
3. that(); // Window { … }
4. that() === window; // true
5.
6. /* In Node */
7. var that = function () { return this; };
8. that(); // { global: …, console: … }
9. that() === global; // true

Nested Functions
42
1. var root = this;
3. function inner () { return this; }
4. var that = inner();
5.
6. console.log(that); // Window { … }
7. console.log(that === window); // true
8. console.log(that === this); // true
9. console.log(that === root); // true
10. }
11.
12. outer();

The Function Constructor
43
1. var self = new Function('return this');
2.
3. self(); // Window { … }
4. self() === window; // true
5. self() === this; // true

Object Methods
44
1. var data = {
2. self: function () {
3. return this;
4. }
5. };
6.
7. data.self(); // {self: function}
8. data.self() === data; // true

Object Methods Refer To Global Functions
45
1. function age () { return this._age; }
2.
3. var dog = { _age: 5, age: age };
4. var cat = { _age: 1, age: age };
5.
6. dog.age(); // 5
7. cat.age(); // 1

Getters And Setters
46
1. var data = {
2. x: 10,
3. get y () { return this.x + 5; },
4. set z (z) { this.x = this.x * z; }
5. };
6.
7. data.z = 3;
8.
9. console.log(data.x); // ?
10. console.log(data.y); // ?
1. var data = {
2. x: 10,
5. };
6.
7. data.z = 3;
8.
9. console.log(data.x); // 30
10. console.log(data.y); // ?
1. var data = {
2. x: 10,
5. };
6.
7. data.z = 3;
8.
9. console.log(data.x); // 30
10. console.log(data.y); // 35

Method Chaining
47
1. [2, 5, 1, 7, 4]
2. .sort(function (a, b) { return a - b })
3. .reverse()
4. .map(function (n) { return n * 10; });
5.
6. // (6) [70, 50, 40, 20, 10]

Chainable Methods
48
1. var list = {
2. items: [3, 8, 5],
3. push: function (value) {
4. this.items.push(value); return this;
5. },
6. remove: function (value) {
7. var index = this.items.indexOf(value);
8. if (index > -1) { this.items.splice(index, 1); }
9. return this;
10. }
11. };
12. list.push(7).push(2).remove(8).items;
13. // (4) [3, 5, 7, 2]

An arrow function does not
create its own this value.
49

Arrow Functions Used As Methods
50
1. var root = this;
2. var object = {
3. origin: function () { return this; },
4. short: () => this
5. };
6.
7. object.origin() === object; // true
8. object.origin() === object.short(); // false
9. object.short() === root; // true

Common Mistake With this
51
1. var zack = {
2. nickname: 'Z',
3. greet: function () {
4. console.log('Hi, I’m ' + this.nickname);
5. }
6. };
7. var greet = zack.greet;
8.
9. greet(); // ?
1. var zack = {
2. nickname: 'Z',
3. greet: function () {
4. console.log('Hi, I’m ' + this.nickname);
5. }
6. };
7. var greet = zack.greet;
8.
9. greet(); // 'Hi, I’m undefined'

Invoking Functions
53
2. return x + y;
3. }
4.
5. add(5, 8); // 13
6. Math.floor(3.14); // 3

Invoking Object Methods
54
1. var employee = {
2. title: 'PM',
3. name: 'Alex',
4. info: function () {
5. return this.name + ' is a ' + this.title;
6. }
7. };
8.
9. employee.info(); // 'Alex is a PM'

Function Call
55
1. var name = 'Window';
2. var jack = { name: 'Jack' }, nick = { name: 'Nick' };
3.
4. function whoami () { return this.name; }
5.
6. whoami(); // 'Window'
7. whoami.call(this); // 'Window'
8. whoami.call(jack); // 'Jack'
9. whoami.call(nick); // 'Nick'
10.
11. [1, 2].concat.call([3, 4], [5, 6]); // ?
1. var name = 'Window';
2. var jack = { name: 'Jack' }, nick = { name: 'Nick' };
3.
4. function whoami () { return this.name; }
5.
6. whoami(); // 'Window'
7. whoami.call(this); // 'Window'
8. whoami.call(jack); // 'Jack'
9. whoami.call(nick); // 'Nick'
10.
11. [1, 2].concat.call([3, 4], [5, 6]); // (4) [3, 4, 5, 6]

Function Apply
56
1. Math.max(5, 2, 7, 4); // 7
2. Math.max.apply(null, [9, 1, 3, 6]); // 9
3.
4. function sum () {
5. return [].slice.call(arguments, 0).reduce((a, b) => a + b);
6. }
7.
8. sum.apply(null, [1, 2, 3, 4, 5]); // 15

The function.bind() Method
57
1. function color () { return this.color; }
2.
3. var yellow = { color: '#ff3' };
4. var purple = { color: '#609' };
5.
6. typeof color.bind(yellow); // 'function'
7. color.bind(yellow)(); // '#ff3'
8.
9. typeof color.bind(purple); // 'function'
10. color.bind(purple)(); // '#609'

Currying
58
2. return x + y;
3. }
4.
5. var add5 = add.bind(null, 5); // Curried
6.
7. add(5, 3); // 8
8.
9. add5(10); // ?
10. add5(60); // ?
2. return x + y;
3. }
4.
6.
7. add(5, 3); // 8
8.
9. add5(10); // 15
10. add5(60); // ?
2. return x + y;
3. }
4.
6.
7. add(5, 3); // 8
8.
9. add5(10); // 15
10. add5(60); // 65

Self-Invoking Functions (Immediately Invoked Function Expression)
59
1. var number = (function (x) { return x + 3; })(7);
2. console.log(number); // 10
3.
4. (() => 'blabla')(); // 'blabla'
5.
6. (function (_) {
7. var title = 'My Home';
8. console.log(window.title); // undefined
9. })(underscore);

A closure is the combination of
a function and the lexical
environment within which that
function was declared.
61

Lexical Scope / Static Scope
62
2. var skill = 'JavaScript';
4. console.log(skill); // 'JavaScript'
5. }
6. inner();
7. console.log(title); // 'Tutorial'
8. }
9. var title = 'Tutorial';
10.
11. outer();

inner()
outer()
global
console.log(skill);
console.log(title);
(NONE)
skill = 'JavaScript'
title = 'Tutorial'
Scope Chain
63
Closures
ScopeChain
Reference to outer lexical enviroment

Closures
64
1. function doubler (n) { return function () { return n * 2; }; }
2. function subtractor (x) { return (y) => (x = x - y); };
3.
4. var sixteen = doubler(8);
5. var subtract = subtractor(100);
6.
7. sixteen(); // 16
8.
9. subtract(15); // ?
10. subtract(20); // ?
3.
6.
7. sixteen(); // 16
8.
9. subtract(15); // 85
10. subtract(20); // ?
3.
6.
7. sixteen(); // 16
8.
9. subtract(15); // 85
10. subtract(20); // 65

1. function doubler (n) {
2. return function () {
3. return n * 2;
4. };
5. }
65
Closure
The instance sixteen maintains a reference to its lexical environment,
within which the variable n exists.

Using Closure To Define Private Properties
66
1. function Circle (radius) {
2. this.getRadius = function () { return radius; };
3. this.setRadius = function (value) { radius = value; };
4. }
5. var circle = new Circle(10);
6.
7. circle.radius; // undefined
8. circle.getRadius(); // 10
9. circle.setRadius(20); // 20
10. circle.getRadius(); // 20

A Common Mistake With Closure
67
1. var i = 0, fn = {};
2.
3. for (; i < 5; ++i) {
4. fn['get' + i] = function () {
5. console.log(i);
6. };
7. }
8.
9. fn.get2(); // ?
1. var i = 0, fn = {};
2.
3. for (; i < 5; ++i) {
4. fn['get' + i] = function () {
5. console.log(i);
6. };
7. }
8.
9. fn.get2(); // 5

Chapter 6.
Constructors And Prototypes
68

Constructors
70
1. function Fruit (name) {
2. this.name = name;
3. }
4.
5. var kiwi = new Fruit('Kiwi');
6.
7. kiwi.name; // 'Kiwi'

Arrow functions cannot
be used as constructors.
71

Arrow Functions Cannot Be Used As Constructors
72
1. var Cloth = (type) => {
2. this.type = type;
3. };
4.
5. new Cloth('Shirt'); // TypeError

Prototype-based Programming
Prototype-based programming is a style of object-oriented programming in
which behaviour reuse is performed via a process of reusing existing
objects via delegation that serve as prototypes. – Wiki
74
Prototypes

The Special Object Properties
75
● object.prototype returns a reference to the prototype for a class of
objects.
● object.__proto__ returns a reference to the internal prototype of the
specified object.
Prototypes

The Prototype Chain Of An Instance
76
1. function Fruit (name) {
2. this.name = name;
3. }
4.
5. var kiwi = new Fruit();
6.
7. kiwi.__proto__ === Fruit.prototype; // true
8. kiwi.__proto__.__proto__ === Object.prototype; // true
9. kiwi.__proto__.__proto__.__proto__; // * null
10.
11. kiwi.__proto__ === Object.getPrototypeOf(kiwi); // true

77
var kiwi = new Object();
kiwi.__proto__ = Fruit.prototype;
Fruit.call(kiwi);
1
2
3
What Does The new Operator Do?
Prototypes
var kiwi = new Fruit();
⇒
return kiwi;4

The Prototype Chain Of A Constructor
78
1. function Dog () {}
2. Dog.prototype.self = function () { return this; };
3.
4. var dog = new Dog();
5.
6. Dog.__proto__ === Function.prototype; // true
7. Dog.__proto__.__proto__ === Object.prototype; // true
8. Dog.__proto__.__proto__.__proto__; // * null
9.
10. Dog.prototype.constructor === Dog; // true
11. dog.constructor === Dog; // true

FunctionsInstances Prototypes
d1
function Function () {}
function Object () {}
function Dog () {}
Function.prototype
Object.prototype
Dog.prototype
var … = new Dog();
d2
o1
var … = new Object();
o2
__proto__
prototype
constructor
null

Creating Objects Using Object.create()
80
1. var animal = { gender: 'Unknown' };
2. var human = Object.create(animal);
3. var female = Object.create(human, {
4. gender: { value: 'Female' }
5. });
6.
7. human.gender; // 'Unknown'
8. human.__proto__ === animal; // true
9.
10. female.gender; // 'Female'
11. female.__proto__ === human; // true
12. female.__proto__.__proto__ === animal; // true

Creating Objects Using Object.create(null)
81
1. var common = {};
2. var uncommon = Object.create(null);
3.
4. common.constructor === Object; // true
5. common.__proto__ === Object.prototype; // true
6.
7. uncommon.constructor; // undefined
8. uncommon.__proto__; // undefined

You can add properties and
methods to the prototype of
built-in objects.
82

Adding Methods To Array.prototype
83
1. Array.prototype.first = function () {
2. return this[0];
3. };
4.
5. Array.prototype.last = function () {
6. return this[this.length - 1];
7. };
8.
9. var numbers = [100, 200, 300];
10.
11. numbers.first(); // 100
12. numbers.last(); // 300

Avoid modifying the prototypes
of standard JavaScript objects.
84

All built-in objects
have a prototype property
that is read-only.
85

Unconfigurable Object Prototypes
86
1. Array.prototype = {
2. first: function () {
3. return this[0];
4. }
5. };
6.
7. var numbers = [100, 200, 300];
8.
9. numbers.first; // undefined
10. Object.getOwnPropertyDescriptor(Array, 'prototype');
11. // {configurable: false, … }

Arrow functions do not have
a prototype property.
87

Arrow Functions Do Not Have A prototype Pproperty
88
1. var Cloth = (type) => {
3. };
4.
5. Cloth.prototype; // undefined

All objects inherit their
properties and methods from
their prototype.
90

Native Prototypes
91
1. (10).toFixed === Number.prototype.toFixed; // true
2. (true).valueOf === Boolean.prototype.valueOf; // true
3. ('A').trim === String.prototype.trim; // true
4. ({}).toString === Object.prototype.toString; // true
5. ([]).concat === Array.prototype.concat; // true

Overriding The Native Prototypes
92
1. var empty = {};
2. var script = { toString: () => 'Script' };
3. var ten = { valueOf: () => 10 };
4.
5. String(empty); // '[object Object]'
6. String(script); // ?
7. 'Java' + script; // ?
8. Number(empty); // NaN
9. Number(ten); // ?
10. ten + 20; // ?
1. var empty = {};
3. var ten = { valueOf: () => 10 };
4.
6. String(script); // 'Script'
7. 'Java' + script; // ?
10. ten + 20; // ?
1. var empty = {};
3. var ten = { valueOf: () => 10 };
4.
7. 'Java' + script; // 'JavaScript'
10. ten + 20; // ?
1. var empty = {};
3. var ten = { valueOf: () => 10 };
4.
9. Number(ten); // 10
10. ten + 20; // ?
1. var empty = {};
3. var ten = { valueOf: () => 10 };
4.
9. Number(ten); // 10
10. ten + 20; // 30

A Custom Object
93
1. function Pig (name) { this.name = name; }
2. Pig.prototype.type = 'Pig';
3. Pig.prototype.sleep = function () { console.log('zZzZ…'); };
4.
5. var piggy = new Pig('Wilbur');
6.
7. piggy.name; // 'Wilbur'
8. piggy.type; // 'Pig'
9. piggy.sleep(); // 'zZzZ…';
10. piggy instanceof Pig; // true
11. piggy instanceof Object; // true

Shared Properties
94
1. function Player () { this.counting(); }
2. Player.prototype.counter = { value: 0 };
3. Player.prototype.counting = function () {
4. ++this.counter.value;
5. };
6.
7. var player1 = new Player();
8. player1.counter.value; // 1
9.
10. var player2 = new Player();

It is recommended to
define methods to all instances
through object prototype.
95

Instance Properties And Prototype Properties
96
1. function Robot () {
2. this.walk = function () {}
3. }
4. Robot.prototype.talk = function () {};
5.
6. var wat = new Robot(), eve = new Robot();
7.
8. wat.walk === eve.walk; // false
9. wat.talk === eve.talk; // true
10. wat.talk === Robot.prototype.talk; // true
11. wat.hasOwnProperty('walk'); // true
12. wat.hasOwnProperty('talk'); // false

Classical Inheritance With Object.create()
97
1. function Bird () {}
2. Bird.prototype.fly = function () {};
3.
4. function Pigeon () { Bird.call(this); }
5. Pigeon.prototype = Object.create(Bird.prototype);
6. Pigeon.prototype.constructor = Pigeon;
7. var pigeon = new Pigeon();
8.
9. Pigeon.prototype.__proto__ === Bird.prototype; // true
10. pigeon.fly === Pigeon.prototype.fly; // true
11. pigeon.fly === Bird.prototype.fly; // true

Override Methods
98
1. function Bird () {}
2. Bird.prototype.fly = function () { return 'Default'; };
3.
4. function Eagle () { Bird.call(this); }
5. Eagle.prototype = Object.create(Bird.prototype);
6. Eagle.prototype.constructor = Eagle;
7. Eagle.prototype.fly = function () { return 'Overrode'; };
8. var eagle = new Eagle();
9.
10. Eagle.prototype.__proto__ === Bird.prototype; // true
11. eagle.fly === Eagle.prototype.fly; // true
12. eagle.fly === Bird.prototype.fly; // false

Class Declarations
100
1. class Bird {
2. constructor (type) {
4. }
5. fly () {
6. console.log('Fly!');
7. }
8. }
9.
10. typeof Bird; // 'function'

Sub Classing With extends
101
1. class Penguin extends Bird {
2. constructor () {
3. super('Penguin');
4. }
5. fly () {
6. super.fly();
7. console.log('Penguin Fly!');
8. }
9. }
10.
11. Penguin.prototype.fly === Bird.prototype.fly; // false

Static Methods
102
1. class Food {
2. static calorie () {}
3. }
4.
5. function Drink () {}
6. Drink.calorie = function () {}

The best thing about JavaScript is
its implementation of functions. It
got almost everything right. But, as
you should expect with JavaScript,
it didn't get everything right.
- Douglas Crockford
103

Reference
105
● JavaScript | CodeData
● Prototype-based programming - Wikipedia
● First-class function - Wikipedia
● JavaScript Guide - JavaScript | MDN
● JavaScript Tutorial | W3Schools

Reference Books
● JavaScript: The Good Parts
● Effective JavaScript
106

Practical JavaScript Programming - Session 3/8

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