Javascript. Daniel Zappala. CS 360 Internet Programming Brigham Young University

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1 Javascript Daniel Zappala CS 360 Internet Programming Brigham Young University

2 Introduction

3 3/35 Introduction Basics Functions Data Structures Higher-Order Functions Prototypes What You Should Read Eloquent JavaScript introductory interactive coding Why Prototypical Inheritance Matters advanced prototypical inheritance

4 Why Javascript? 4/35 client-side computation more responsive web user interface asynchronous communication with server dynamically change HTML being displayed by browser built into most browsers

5 Javascript vs Java 5/35 JavaScript has no relationship to Java Javascript is becoming what Java was meant to be lightweight, downloadable program that runs in browser and is compatible across many platforms does much of what Java applets do, with a fraction of the resources

6 Features 6/35 interpreted dynamic typing (delays binding of types until they are used) first-class functions (can take functions as arguments and return functions) prototypes (objects based on prototypes instead of inheritance)

7 Hello World 7/35 1 alert("hello world!");

8 Functions 8/35 1 var factorial = function(n) { 2 if (n === 0) { 3 return 1; 4 } 5 return n factorial(n 1); 6 } 7 factorial(5);

9 DOM Parsing and Manipulation 9/35 1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" " w3.org/tr/html4/strict.dtd"> 2 <html> 3 <meta charset="utf-8"> 4 <head> 5 <title>simple page</title> 6 </head> 7 <body> 8 <h1 id="header">this is JavaScript</h1> 9 <script type="text/javascript"> 10 document.write( Hello World! ); 11 // get element with CSS ID "header" 12 var h1 = document.getelementbyid("header"); 13 console.log(h1.innerhtml); 14 // get first h1 on the page 15 h1 = document.getelementsbytagname("h1")[0]; 16 console.log(h1.innerhtml); 17 // change element 18 h1.innerhtml = "This is dope!"; 19 </script> 20 </body> 21 </html>

10 Basics

11 Variables 11/35 1 // local variable 2 var x = 12; 3 // global variable 4 y = 12;

12 Operators 12/35 comparison 1 > 2 < 3 >= 4 <= 5!= 6 == 7! 8 9 && 10 === // no automatic type conversion 11!== // no automatic type conversion

13 Operators 13/35 expressions and assignment / 5 % 6 = 7 += 8 =

14 Control 14/35 1 if ( boolean statement ) { } else { } 1 switch (variable) { 2 case 1: break; 5 case 2: break; 8 case default: break; 11 }

15 Control 15/35 1 while (boolean condition) 2 { } 1 do 2 { } 5 while (boolean condition); 1 for (var i = 0; i < 10; i++) { }

16 Functions

17 Functions 17/35 1 var add = function(a,b) { 2 return a + b; 3 } 4 5 add(5,3);

18 Scope 18/35 1 var landscape = function() { 2 var result = ""; 3 var flat = function(size) { 4 for (var count = 0; count < size; count++) 5 result += "_"; 6 }; 7 var mountain = function(size) { 8 result += "/"; 9 for (var count = 0; count < size; count++) 10 result += " "; 11 result += "\\"; 12 }; flat(3); 15 mountain(4); 16 flat(6); 17 mountain(1); 18 flat(1); 19 return result; 20 }; console.log(landscape()); 23 // / \ / \_

19 Optional Parameters 19/35 1 function power(base, exponent) { 2 if (exponent == undefined) 3 exponent = 2; 4 var result = 1; 5 for (var count = 0; count < exponent; count++) 6 result = base; 7 return result; 8 } 9 10 console.log(power(4)); 11 // console.log(power(4, 3)); 13 // 64

20 Closure 20/35 1 var increment = function() { 2 var count = 0; 3 return function () { 4 return ++count; 5 }; 6 } 7 console.log(increment()); 8 // 1 9 console.log(increment()); 10 // 2

21 Data Structures

22 Lists 22/35 1 var list = [2, 3, 5, 7, 11]; 2 console.log(list[1]); 3 // 3 4 console.log(list.length); 5 // 5 6 list.push(13,17); 7 console.log(list); 8 // [ 2, 3, 5, 7, 11, 13, 17 ]

23 Objects 23/35 1 var user = { 2 loggedin: false, 3 items: ["homework", "read The Martian", "play frisbee golf"], 4 whatshouldido: function() { 5 return "You should be doing " + this.items[0] 6 } 7 }; 8 console.log(user.loggedin); 9 // false 10 console.log(user.name); 11 // undefined 12 user.name = "Emma"; 13 console.log(user.name); 14 // Emma 15 console.log(user.whatshouldido()); 16 // You should be doing homework

24 Higher-Order Functions

25 foreach 25/35 executes a function for each element in a list 1 var pets = ["dog","cat","lizard"] 2 pets.foreach(function(pet) { 3 console.log(pet.touppercase()); 4 }); 5 // DOG 6 // CAT 7 // LIZARD

26 filter 26/35 returns a new list by applying a function that checks for membership 1 var housepets = pets.filter(function(pet) { 2 return (pet === "dog" pet == "cat"); 3 }); 4 console.log(housepets); 5 // [ dog, cat ]

27 map 27/35 creates a new list by applying a function to transform all elements 1 var uppers = pets.map(function(pet) { 2 return pet.touppercase(); 3 }); 4 console.log(uppers); 5 // [ DOG, CAT, LIZARD ]

28 reduce 28/35 returns a value by applying a function to all elements 1 var total = pets.map(function(pet) { 2 return pet.length; 3 }).reduce(function(a,b) { 4 return a + b; 5 }); 6 console.log(total); 7 // 12

29 Prototypes

30 Prototypes 30/35 Object.create() clones an object, specifying its prototype 1 var rectangle = { 2 area: function () { 3 return this.width this.height; 4 } 5 }; 6 var rect = Object.create(rectangle); 7 rect.width = 5; 8 rect.height = 10; 9 console.log(rect.area()); see Why Prototypical Inheritance Matters

31 Simplifying Object Creation 31/35 wrap create into a function 1 var rectangle = { 2 create: function (width, height) { 3 var self = Object.create(this); 4 self.height = height; 5 self.width = width; 6 return self; 7 }, 8 area: function () { 9 return this.width this.height; 10 } 11 }; 12 var rect = rectangle.create(5, 10); 13 console.log(rect.area());

32 Overriding Functions 32/35 square calls its own create(), which calls create() of rectangle square calls area() on rectangle 1 var square = Object.create(rectangle); 2 3 square.create = function (side) { 4 return rectangle.create.call(this, side, side); 5 }; 6 var sq = square.create(5); 7 console.log(sq.area());

33 Extending Objects 33/35 extend() creates a new object that inherits properties from this (delegation) and copies properties from extension (concatenation) 1 Object.prototype.extend = function (extension) { 2 var hasownproperty = Object.hasOwnProperty; 3 var object = Object.create(this); 4 5 for (var property in extension) 6 if (hasownproperty.call(extension, property) 7 typeof object[property] === "undefined") 8 object[property] = extension[property]; 9 10 return object; 11 };

34 Extending The Square 34/35 extends rectangle with create 1 var square = rectangle.extend({ 2 create: function (side) { 3 return rectangle.create.call(this, side, side); 4 } 5 }); 6 7 var sq = square.create(5); 8 9 console.log(sq.area());

35 Extending The Rectangle 35/35 extends Object with height, width 1 var rectangle = { 2 create: function (width, height) { 3 return this.extend({ 4 height: height, 5 width: width 6 }); 7 }, 8 area: function () { 9 return this.width this.height; 10 } 11 }; var rect = rectangle.create(5, 10); 14 console.log(rect.area());

JavaScript: Introduction, Types

JavaScript: Introduction, Types Computer Science and Engineering College of Engineering The Ohio State University Lecture 19 History Developed by Netscape "LiveScript", then renamed "JavaScript" Nothing