1 Standard based web design Overview of Dynamic HTML.

transcript

Standard based web design

Overview of Dynamic HTML

What is DHTML?

Dynamic Hypertext Markup Language is comprised of: CSS (cascading style sheets) DOM (document object module) Scripting (Javascript and VBscript)

Allows for more interactivity and special effects on web pages.

Document Object Model (DOM)

DOM is an interface that permits scripts to access and update the content, structure and style of the document.

Every element of the web page can be dynamically updated in response to input from the user or other programs

HTML elements are treated as objects, their attributes are treated as properties of the objects

The DOM has a hierarchy of elements with the window as the top level object

Object hierarchy: an example

window.document.formNamedocument.formName

JavaScript

JavaScript is an object-based language: it is based on manipulating objects by modifying their properties or applying methods to them.

Objects are items that exist in a defined space in a Web page (window, document, form etc)

Each object has properties that describe its appearance, purpose, or behavior

An object can have methods, which are actions that can be performed with or to it.

JavaScript and events Certain objects and tags in HTML

have corresponding events associated to them. A button in a form can be clicked

JavaScript allows you to trigger action based on an event taking place, by using event handlers onClick do this and that

JavaScript and HTML Place JavaScript commands in a separate file & link the

HTML file to that file by using the <SCRIPT> tag in the head of the file

<SCRIPT SRC=URL LANGUAGE=“javascript”>other script commands and comments

</SCRIPT>

Place JavaScript commands directly in the HTML file (<SCRIPT> tag in the <HEAD> or the <BODY>)

script commands and comments

</SCRIPT>

<!- - Hide this script from browsers that don’t support JavaScript// Stop hiding from other browsers - ->

A trivial example

document.lastModified reflects when the page was last modified document is the objectlastModified is a property of document <script languange=“javaScript”>var modifiedDate=document.lastModified;document.write(modifiedDate);</script>

The window object and methods

The window object represents a browser window. Window methods are window.alert("string“); Shows an alert window

with text string, and 'OK' button window.prompt(“string of character”, “default value”);

Prompts user for input Window.confirm(“string”);If the OK button is

clicked, the confirm method returns the value “true” window.close(); window.open(URL, windowname);

Objects and their methods

JavaScript events

An event is a specific action that triggers the browser to run a block of JavaScript commands

Event handlers

Working with object properties

Change the value of a property object.property = expressiondocument.bgColor=“red”

Save object property as a variablevariable = object.propertypageColor =document.bgColor

JavaScript event handlers An event handler is code added to an

HTML tag. It is triggered when the associated event occurs within the tag

<FORM><INPUT TYPE=RADIO onClick=“document.bgColor=‘red’;”>red<BR><INPUT TYPE=RADIO onClick=“document.bgColor=‘blue’;”>blue<BR></FORM>INPUT is the tag, onClick is the event, “document…” is the event handler

Coming up Form validation Mathematical manipulations Changing style: visibility,display,clip

(menus) Repeating commands (Slide shows,

banners) Filters and transitions Moving object on the screen

Validating forms

You can use JavaScript to Make sure that your form contain valid

information Check data in one field against data in

another field (choose a new password) Highlight incorrect information to let

the user know what needs to be changed

Your name: <INPUT TYPE="TEXT" SIZE="30">

<P>Choose a password: <INPUT TYPE="PASSWORD" NAME="passwd1">

<P>Verify password: <INPUT TYPE="PASSWORD" NAME="passwd2">

</FORM>

•If passwd1 ==“”tell the user to enter a password and reposition the cursor to the correct field

•If passwd1!=passwd2tell the user the 2 passwords don’t match and reposition the cursor

Form Validation

onSubmit=“return checkform(this)”

function validForm(passForm) {

if (passForm.passwd1.value == "") {

alert("You must enter a password");

passForm.passwd1.focus();

return false}

else {

if (passForm.passwd1.value != passForm.passwd2.value) {

alert("Entered passwords did not match");

passForm.passwd1.focus(); //return the cursor to the first password field

passForm.passwd1.select(); //select the entry in the first

password field

return false}

else {return true}

}<FORM NAME="changePsw" onSubmit="return validForm(changePsw)" >

<FORM onSubmit="return validForm(this)" >or

More on forms Copying the values entered in one

field to another field Convert F degrees into Celsius A mortgage calculator

Microsoft Object Hierarchywindow

document

history

navigator

applets

anchors

embeds

filters

images

plugins

styleSheets

scripts

location

screen

document

plugins

object

collection

frames

Only in IE

Netscape DOM

Element collections In JS you translate this hierarchy into

reference names which indicate the location of the element in the DOM

Elements can be grouped into element collections which are arrays of all the elements of a particular type

document.images.myImageID.propertydocument.images[“myImageID”].property

Referencing <DIV> tagsNetscape (<div>s belong to the layers collection)document.layers.divID or document.divID

I.E. (<div>s belong to the all collection)document.all.divID or divID

Browser detection:var isNS=false; // True if user has Netscapevar isIE=false; // True if user has Internet

Explorerif (document.layers){isNS=true;}if (document.all){isIE=true;}

Referencing StylesThe syntax rules for changing one of the style

attributes of an element in Netscape: objectID.attributeI.E. objectID.style.attribute objectID is the name of the particular

element (image, div, form field ..), style is a JS word, attribute is the specific attribute you are referring to (visibility, display …)

The attribute can’t contain “-”!background-color becomes backgroundColor

W3C DOM (a farewell to DOM)

The W3C DOM doesn’t use the dot syntax to describe objects

The programmers uses the ID attribute (instead of NAME) to name each element in advance<IMG ID=myImage>

Use the getElementByID(tagID) tool to access that element document.getElementByID(“myImage”)

Netscape 6, IE 5+, Opera 5+ etc

Controlling object visibility

Internet Explorerdocument.getElementById(“id”).visibility=“visible/

hidden”;

document.getElementById(“id”).display=“none”;document.getElementById(“id”).display=“block”;document.getElementById(“id”).clip=“rect(t,r,b,l)”

Before clipping

After clipping

Menus Side menu: MSNBC

MetraRail Drop Down: T-Mobile

In-Style Magazine

Rollovers DePaul website Bloomingdale’s wedding channel CBS

Repeating commands

clearInterval (variable);

tells the script to run the function fctName at the specified interval of milliseconds.

variable=setInterval(“fctName()”,# of millisec);

Cancels the setInterval command

Time delayed commands

variable= setTimeout(“fctName()”,# of millisec);

tells the script to run the function fctName after the specified number of milliseconds

clearTimeout (variable);

Cancels the time delayed command

Cycling banner ads (images)

adImages is an array containing the URLs of the banner images

adBanner is the name in the <IMG> tag where the ads are displayed

function next(){…document.adBanner.src=adImages[counter];setTimeout(“rotate()”,3*1000);…}

Every 3 seconds the src of the image tag is updated

Photo gallery and slide shows Prev-Next: Chicago tribune Automatic show: MSNBC

Other effects Scrolling news: metrarail Filters Increasing font size Cursor Images

Transition (special filters) A transition is a visual effect applied to an object

over an interval of time blendTrans fades an object in and out. You have

to specify a value for the Duration of the transitionobjectName.filters.blendTrans.Duration =2;

orobjectName.style.filter=“blendTrans(Duration=2)”;

revealTrans in addition to the Duration it allows you to specify the type of the transition

objectName.filters.revealTrans.Duration=2; // 2 seconds

objectName.filters.revealTrans.Transition=5; //Wipe down

orobjectName.style.filter=“revealTrans(Duration=2, Transition=5)”;

Applying a transition1. Set the initial state of the object

(visibility, or source for an image file)2. Apply a transition effect to the object

(by using the apply() method)objectName.filters.transition_type.apply();

3. Specify the final state of the object4. Play the transition (use the play() method)

objectName.filters.transition_type.play();

Moving objects on the screen Once an object is positioned in the

HTML code using the position attribute in CSS, you can change the coordinates of the object using JavaScript attributes

objectID.style.left or objectID.style.tophow far the left/top edge of the object is from the parent element (100px).The value of these attributes may be changed dynamically

function moveObjectTo(objectID,x,y){ moverObject=document.getElementById(objectID).style; moverObject.left =x; moverObject.top =y; }<IMG id=“mover” onClick=“moveObjectTo(mover,100,100)>

Moving objects on the screen

function slide(){ moverObject =document.getElementById(“mover”).style; moverObject.pixelLeft =moverObject.pixelLeft +2; if (moverObject.pixelLeft <= rightDotPos){ setTimeout(“slide()”, 20);} <BODY onLoad=“slide()”><IMG ID=“mover” src=fullmoon.jpg>

Window height and widthIE: document.body.clientHeight document.body.clientWidthAre the body properties that indicates the

dimension of the browser window. They are available only after the page is loaded.

Netscape: window.innerHeight window.innerWidth

Properties of the screen object will capture the dimension of the user’s monitor

Linear animation (diagonally across)

function moveText(){maxHeight = document.body.clientHeight –100; moverObject =document.getElementById(“mover”).style;moverObject.pixelLeft =moverObject.pixelLeft +2; moverObject.pixelTop =moverObject.pixelTop +2;

if (moverObject.pixelLeft <= maxHeight){ setTimeout(“moveText()”, 20);} }

<DIV ID=mover”> On the Road again </DIV>

<STYLE>#mover {position:absolute;left:5px;top:5px;}</STYLE>

Path animation You are not restricted to linear

paths for animation. You can have the object move from point to point along a path that has any shape you want

The x coordinate of each point in the path is stored into an array (x)

The y coordinate of each point is stored into another array (y)

Path animation (spiral in)

function moveIt(objectID,dx,dy){moverObject =document.getElementById(objectID).style;moverObject.pixelLeft =moverObject.pixelLeft +dx; moverObject.pixelTop =moverObject.pixelTop +dy;}

//store the consecutive increments in x and y (dx, and dy)x= new Array(0,20,40,80, … -100,-50, …);y= new Array(0,10,20,40, … -150, -80, …);index=0;

Function spiral(){ if (index <x.length-1){ moveIt(“mover”,x[index],y[index]); index++; setTimeout(“spiral()”, 100);} }

End of Lecture

1 Standard based web design Overview of Dynamic HTML.

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