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Put on by USC's Upsilon Pi Epsilon as part of Wonderful World of Web2.0 Workshop Series. http://pollux.usc.edu/~upe/
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
<script><script>… … JavaScript code goes here… JavaScript code goes here… </script></script>
• 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>
JavaScript: the basics
<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>
JavaScript: the basics
•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
JavaScript: Functions
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
JavaScript: Functions
function avg() {function avg() { var sum = 0;var sum = 0; for (var i=0, j=arguments.length; i<j; i++) for (var i=0, j=arguments.length; i<j; i++) {{ sum += arguments[i];sum += arguments[i]; }} return sum/arguments.length;return sum/arguments.length;}}
> 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
JavaScript: Functions
•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
function Person(first, last) {function Person(first, last) { this.first = first;this.first = first; this.last = last;this.last = last; this.fullName = function() {this.fullName = function() { return this.first + ' ' + this.last;return this.first + ' ' + this.last; }} this.fullNameReversed = function() {this.fullNameReversed = function() { return this.last + ', ' + this.first;return this.last + ', ' + this.first; }}}}var ross = new Person("Ross", "Boucher");var ross = new Person("Ross", "Boucher");
JavaScript: Classes•Previous method duplicates member
functions for every instance•Alternate approach to creating a class:
function personFullName() {function personFullName() { return this.first + ' ' + this.last;return this.first + ' ' + this.last;}}function personFullNameReversed() {function personFullNameReversed() { return this.last + ', ' + this.first;return this.last + ', ' + this.first;}}function Person(first, last) {function Person(first, last) { this.first = first;this.first = first; this.last = last;this.last = last; this.fullName = personFullName;this.fullName = personFullName; this.fullNameReversed = personFullNameReversed;this.fullNameReversed = personFullNameReversed;}}
JavaScript: Classes•Still another approach, using
Prototype:
function Person(first, last) {function Person(first, last) { this.first = first;this.first = first; this.last = last;this.last = last;}}Person.prototype.fullName = function() {Person.prototype.fullName = function() { return this.first + ' ' + this.last;return this.first + ' ' + this.last;}}Person.prototype.fullNameReversed = function() {Person.prototype.fullNameReversed = function() { return this.last + ', ' + this.first;return this.last + ', ' + this.first;}}var ross= new Person(“Ross”, “Boucher”);var ross= new Person(“Ross”, “Boucher”);
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!
