JavaScript Workshop

transcript

Sponsored byUpsilon Pi Epsilon

The Computer Science Honors Society

Javascript

JavaScript: a brief history

• Developed by Netscape Communications Corporation as Mocha, then LiveScript, and finally renamed to JavaScript. • JavaScript was first introduced in Netscape version 2.0B3 in 1995. • In Internet Explorer, “JavaScript” is implemented as JScript, which is not exactly the same.• The latest version of the language is JavaScript 1.7.• ECMAScript is a standardized version of JavaScript.

JavaScript: the basics

• Code Sits Between <script> tags• C/Java style syntax, for the most part• LOOSELY TYPED - more on this later• Can reside in external file also:<script <script src=”someJSFile.js”src=”someJSFile.js”></script>></script>

<html> <html> <head><head><title>… the title of the document… </title> <title>… the title of the document… </title> <script type="text/Javascript"><script type="text/Javascript">… … JavaScript code… JavaScript code… </script> </script> </head> </head> <body><body>… … HTML Code/Tags/Content whatever… HTML Code/Tags/Content whatever… </body> </body> </html></html>

•Event Handlers •(most basic html interaction tool)•“onclick”, “onmouseover”, “

onmouseout”, “onload”, “ondoubleclick”, etc.

•Written in the HTML as an attribute

JavaScript: Hello World

<html> <html> <head><head><title>JavaScript-Hello-World</title> <title>JavaScript-Hello-World</title> <script type="text/Javascript"> <script type="text/Javascript">

function greetings(sender) {function greetings(sender) {alert (“Hello World!”); alert (“Hello World!”); } }

</script> </script> </head></head><body <body onLoad="greetings();“onLoad="greetings();“> > <h1>Javascript Hello World!</h1> <h1>Javascript Hello World!</h1> </body> </body> </html></html>

JavaScript: Challenge!• Create a web page with a header that says “Hello

World...”.• When the user roles over the header, change the

text to read “Hello JavaScript!”.• Use an external JavaScript file.• Hint: Use Google to look up “onmouseover”• Hint: Event handlers can pass objects -- think of

the header as an object itself (a DOM object)• Hint: DOM Objects have an “innerHTML” property• Bonus: Change the font and background color

when you role over the text• Be Creative! Add whatever you want, we’ll help.

JavaScript: Types• Number

• String

• Boolean

• Object

• Function

• Array

• Date

• RegExp

• Null

• Undefined

• Variables can hold any type!

JavaScript: Numbers•All numbers are 64 bit floating point

(IEEE)•Familiar parseInt(“123”) syntax to get a

number from a string•Math object contains advanced math

functions•NaN is returned in any operation that

does not result in a valid number•Special Infinity and -Infinity values

JavaScript: Strings•Really just Objects (like almost

everything)•Sequences of Unicode characters•Built-in length, charAt(),

toUpperCase() and other properties•“string literals” are also present

JavaScript: Other Types

•Bools -- just what you think•RegExp -- Regular Expression

Objects•Null -- deliberate “no” value for an

arbitrary variable •Undefined -- variable that has not

even been initialized

JavaScript: Operators•Same as C/C++/Java: ++, +=, +, -, /, *,

“string”, bitwise and/or/not, &&, ||, !, etc...•Boolean expressions •== performs type coercion•0 == False .... “dog” == True•=== is literal comparsion•False === False .... “dog” !== True

•If, Else, For, While, DoWhile, Switch -- same

JavaScript: Objects•In JavaScript, all objects are

collections of name value pairs.•C++ Hash Table, PHP Associative

Array, Cocoa/Python Dictionary •“Name” is a JavaScript string•“Value” is any JavaScript type,

including other Objects

JavaScript: Objectsvar obj= new Object();var obj= new Object();

var Obj { };var Obj { };

Create

obj.name= “John”;obj.name= “John”;

obj[“name”]= “John”;obj[“name”]= “John”;

Add Properties

Object Literal Syntax

var email {var email {message: “Hi Pamela!”,message: “Hi Pamela!”,details: {details: {to: “Pamela”,to: “Pamela”,from: “Ross”from: “Ross”}}}}

JavaScript: Arraysvar a= new Array();var a= new Array();a[0]= “red”;a[0]= “red”;a[1]= “blue;a[1]= “blue;

var a= {“red”, “blue”};var a= {“red”, “blue”};

Create

• Full-fledged JavaScript Objects themselves• Built-in Length property = highest index + 1• Other Built-in methods:a.toString(), a.toLocaleString(), a.concat(item, ..), a.join(sep),a.pop(), a.push(item, ..), a.reverse(), a.shift(), a.slice(start, end),a.sort(cmpfn), a.splice(start, delcount, [item]..), a.unshift([item]..)

JavaScript: Functions

•Very flexible system -- functions are all JavaScript Objects

•Can take any number of named parameters•Parameters not required to be passed in•More parameters can be passed than asked

for in your function•Return either an explicit value, or

undefined

function add(x, y) {function add(x, y) { var total = x + y;var total = x + y; return total;return total;}}

> add()> add()NaNNaN> add(2, 3)> add(2, 3)55

> avg(2, 3, 4, 5)> avg(2, 3, 4, 5)3.53.5> avg.apply(null, [2, 3, 4, 5])> avg.apply(null, [2, 3, 4, 5])3.5 3.5

•You can assign functions to variables, and do all kinds of crazy things with scope:

•Example, when you say in HTML:•<a onclick=”foo()” id=”bar”></a>

• It’s just like saying bar.onclick= foo in JS

JavaScript: Classes• JavaScript “Classes” are just functions that

initialize new objects (think “constructors”)•“this” refers to the “current” object•“new” is similar to C++ -- call it on

“constructor” functions

JavaScript: Classes•Previous method duplicates member

functions for every instance•Alternate approach to creating a class:

JavaScript: Classes•Still another approach, using

Prototype:

JavaScript: Prototype

•Prototypes are a set of properties shared across all objects of the same type

•In this case, all “Person” objects will have the two methods assigned to Person.prototype

•Forms part of a “lookup chain”•Can add to the prototype of built-in objects•Not to be confused with the library of the

same name

JavaScript: DOM•document is a built in object for

interacting with the DOM•document.getElementById(“string”)

allows you to get a reference to a specific node in your document

•document.createElement(“tag”) allows you to create new elements

•document.createNode(“text”) allows you to create new text nodes

JavaScript: DOM•Documents are made up entirely of nodes•Element Nodes: every tag in your HTML is

an element•Have children nodes, attributes

•Text Nodes: these contain text, and are children of elements like <p> nodes•Have no children or attributes

•Nodes have common methods•nodeType, nodeName, nodeValue

JavaScript: Challenge 2!• Wow, that was a lot of material. Let’s try applying

it!• Create a container DIV, and a few floating divs

inside (hint: assign these inner divs to a class)• Make this look like a few boxes inside a larger box.• Add a link or form button to dynamically add new

divs inside the container (also floated)• Hint: give your container a unique ID so you can

access it with document.getElementById(“myId”);• Hint: use an event handler on the button• Hint: google appendChild()• Bonus: Apply a different style to added divs• Bonus++: Apply a different style every time!

JavaScript Workshop

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