javascript
TRANSCRIPT
INFSCI 1052
Client Side versus Server Side Server side
• PHP, ASP, Cold Fusion, Ruby on Rails• Good for accessing databases
Client Side• Good for immediacy of action• Forms• WebPages• Also, Flash, Ajax
Compiled versus interpreted languages• C, C#, JAVA, • JS, PHP, Python
Adding JS to a webpage• Usually add to the <head> section• Can be added to the <body> section too• Can be linked to an external JS file
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html;
charset=utf-8" /> <title>Untitled Document</title> </head> <script type="text/javascript"> alert('helloworld'); </script> <body> </body> </html>
External Linking to JS File- Two separate lines
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head> <meta http-equiv="Content-Type" content="text/html;
charset=utf-8" /> <title>Untitled Document</title>
<script type="text/javascript" src="myprogram.js"> </script>
<script type="text/javascript"> alert('helloworld'); </script> </head>
<body> </body> </html>
Linking and paths• Absolute paths
http://www.sis.pitt.edu
• Root-relative paths Using a webserver Relative to the site’s top level folder
Ex. /myfolder/index.html
• Document-relative paths Specifies path from Web page to the JS file
Ex: ../myscripts/myjsfile.js
JavaScript:The Missing Manual http://www.sawmac.com/js/tutorials/e
xamples/index.html Completed tutorials section and
working tutorials Focus is on basic JS and using JS
libraries such as JQuery.
Writing text to a web page• Document.write (‘<p> Hello World </P’);• 1.2.html
Attaching external file• 1.3.html
Errors and debugging• If error in code typically nothing happens
Web Browsers have consoles that can display JS errors
Firefox has better console than IE• Lists type of error, name of file, and line number• Select Tools->Error Console
Common Errors• Missing semicolon, missing quote mark, misspelled
word, missing ), unterminated string literal, missing }
Statement: the basic unit of JS program, ends in semicolon
Data Types• Number
Integer or fractional• String
Use quote marks• Boolean
True or False
Variables• Var varname;
Begin with letter, $, or __ Can only contain letters, numbers, $ and __ CaSE SENSITIVE
Var Examples• var number=0;• var name=‘Bob’;• var age=26;• var open=true;
Math operators and order of operations apply• +, -, *, / • Use parenthesis to ensure correct order of
operations
Addition and concatenation• + sign for both purposes• When adding two numbers the + sign does
addition• When “adding” two string or a number and a
string then the concatenation function is performed Ex. var fname = ‘Bill’; var lname = ‘Smith’; var totalname=fname+lname;
Sample: 2.1.html
Arrays• var months = [‘Jan’, ‘Feb’, ‘Mar’];• var months = new Array(‘Jan’, ‘Feb’, ‘Mar’];• Empty array
var months =[];• Accessing arrays
nameofarray[#]; Zero based so nameofarray[2] references the third
element• Adding element to end of array
Nameofarray[nameofarray.length] = ‘text’; Var colors = [‘red’, ‘blue’, green’]
Colors = [colors.length]=‘purple’;
Arrays• Push command to add multiple elements to the array
colors.push(‘pink’, orange’, ‘brown’);• Add to the beginning of an array
.unshift• Push and unshift return a value: the number of items in
the array• Removing items in an array
pop() – removes the last item shift() – removes the first item Ex. var x = [0,1,2,3]; var removeditem = x.pop()
• Adding and deleting in middle of array splice function
• Sample: 2.3.html
Logic
If (condition) {Code statements}
• Comparison operators• >, <, >=, <=
• If else and if else if• && = and • || = or• ! = not• Sample: 3.1.html
Loops• While
while (condition) {JS statements
}
• For Loopsfor (var=x, x<=100; x++) {
JS statements}
Do While Loopsdo {
JS statements} while (condition);
• Sample: dowhile loop
FunctionsFunction functionName() {
JS Statements}
Sample: 3.2.html Send information to functions via
arguments and paramaters
function functionName ( paramater 1, paramater2) {JS Statements};
functionName (argument1, argument2);
• Retrieving Information from functions• Function functionName (paramater1, paramater2) {• JS statements• Return value; • }
• Sample: 3.3.html
DOM• Document Object Model• Working with Web pages
Identify an element on a page Do something with the element
Add/remove a class attribute Change a property of the element Add new content Remove the element Extract information from the element
Provides the information that JS needs to interact with elements on the webpage
A navigation structure or map of the elements on the webpage
Standard from the W3C• Most browsers have adopted but in different
ways Hierarchical structure of the tags in a
web page
Tags• Parents• Chidren• Siblings• All nodes• Text is nodes too• Nesting determines the relationships
Selecting a page element• getElementById()
Locating a single element that has a unique ID document.getElementById(‘header’)
Searches page for a tag with an ID of ‘header’ Typically the results of this action are stored in a variable
var headNode=document.getElementById(‘header’);
GetElementsByTagName• document.getElementsByTagName (‘a’);
Usually stored in a var var myLinks=document.getElementsByTagName
(‘a’); Find all <a> tags and store results in a var named
myLinks This action returns a list of nodes instead of a single
node Similar to arrays
Can access a single node using index notation Can use the length property Can loop using a for loop
Accessing near by nodes• .childNodes
A property of a node Ex.
var headline = document.getElementById(‘header’);var headlineChildren = headline.childNodes;
• .parentNode• A property that represents the direct parent of a node
• .nextSibling and .previousSibling• Properties that access next and previous siblings
• .innerHTML Not a standard part of DOM but most browsers implement it Accesses the text part of a node
Examplevar pTags = document.getElementsByTagName(‘p’);
var theP = pTags[0]; alert(theP.innerHTML);
Opens an alert box and prints out the text of the first paragraph.
JavaScript Quiz• quiz.html
JavaScript Libraries• Small file size• Web oriented• Tested• Free• Large developer community
Jquery.js is a single file that you download that you link to a Web page• http://docs.jquery.com/Downloading_jQuery
Uncompressed – includes comments Minified – compression
Browser downloads the file once and caches it After downloading the file place the library file in
your project Link this file to your web page
<script type=“text/javascript” src=“js/jquery.js”></script>
Once linked write your javascript program
Example:• <script type=“text/javascript”
src=“js/jquery.js”></script>
• <script type=“text/javascript”> Javascript code here
• </script>
• Note: here we created a folder called js and put the downloaded jquery.js file in it.
Selecting page elements• CSS Selectors
Use the jQuery object to select elements $(‘css-selector’) Can use all CSS 2.1 selectors Ex: $(‘#header’) Typically used to select ID’s, classes and element
selectors
ID Selector• <p id=“key”>The key point </p>• var keyparagraph=document.getElementById
(‘key’);• Or• var keyparagraph=$(‘#key’);• Timesaver
Element Selector• var mylist=$(‘a’);
Class selector• var mystuff= $(‘.classthings’)
Selects all elements with same class name
Advanced selectors• Descendent selectors
$(‘#header a’)• Child selectors
$(‘body > p’)• Adjacent siblings• Attribute selectors
More advanced selectors not supported by all browsers just as in CSS
Jquery Selections• Not like the DOM based results• Can’t use traditional DOM methods on them
Ex innerHTML will not work• Most DOM based actions have JQuery
equivalent Automatic Looping
• Jquery functions have looping built-in $(‘#slideshow img’).hide();
Automatically slects all images inside of div tag with ID slideshow and hides images
Chaining• Ability to perform several operations on a
selection of elements• Ex:
$(‘#popUp’).width(300).height(300).text(‘Message’).fadeIn(1000); Sets width and height and adds text and fades inside
div with ID popUp Chaining with the period
Some functions• .html
Works like innerHtml Read current element ( can retrieve what is in an
element) Replace info in current element $(‘#header’).html(‘<p> Look at me I’m a new
header</p>);
• .remove Replace or remove an element $(‘#footer’).remove;
What else can Jquery do?• Select elements• Change value of elements• Replace elements• Remove elements• Change value of elements attribute• Add a class to a tag• Change a CSS property• Get the value of an attribute
Functions• .addClass and .removeClass
Adds a specified class to an element Of course the newly added CSS class must have been
written .removeClass removes a class
• .css Change CSS property
$(‘body’).css(‘padding’,50); .attr
Read/Set an element attribute var attributeinfo=$(‘banner img’).attr(‘src’); Reads and stores the src attribute of the image in the
banner A second argument would set the src
Example• Using .each• this• .clone• .addClass• .removeClass• .before
pullquote
Events$(document).ready(function() {
Code here
});• Makes sure the html of the page loads before
the Javascript runs.• Two step process
• 1) Identify the page element you wish to respond to
• 2) Assign an event and define a function to run when event occurs
Events• Mouse Events
click dblclick mousedown mouseup mouseover mouseout
• Document Window Events Load Resize Scroll Unload
• Form Events Submit Reset - button Change Focus – enter a field Blur – exit a field
Events• Keyboard Events
keypress keydown Keyup
Using Events with Jquery• 1) Select element• 2) Assign an event
$(‘a’).mouseover(); - adds mousever to every link • 3) Pass a function to event
$(‘a’).mouseover(startSomething()); Or pass an anonymous function$(‘a’).mouseover (function() {Code here});
Example:• desecendent selectors• .mouseover• anonymous function• .addClass• .mouseout
Example:• Table.html
Events• When web browser fires an event information is
stored about the event in an event object Vertical and horizontal coordinates the element when event occurred The event object is available to the function handling
the event• Ex
$(document).click(function(evt){ var xPos=evt.pageX; var yPos=evt.pageY; });
Note: evt is not a keyword – use any word
Stopping an event’s normal behavior• Evt. preventDefault();• Ex. To prevent a link being clicked and
moving off the page