© Park University, 2006 Creating an Interactive Web Page with DHTML and JavaScript Park University.

© Park University, 2006

Creating an Interactive Web Page with DHTML and

JavaScriptPark University


Topics• Core Learning Outcomes:

– #2 Demonstrate creativity and problem-solving skills.

– #4 Debug and test Web programs. – #5 Write Web pages and programs that use

proper style. – #6 Write Web pages and Web programs

that use: XHTML, JavaScript, CSS, DHTML

• Topics included in this tutorial:– DHTML


DHTML• A dynamic HTML document (DHTML) is:

– one whose tag attributes, tag contents, or element style properties can be changed after the document has been downloaded, and is still being displayed by a browser

– Uses a combination of HTML, CSS, and JavaScript


Element Positioning• Positioning was covered with CSS.

– CSS-P is CSS Positioning – where CSS is used to position elements (absolute, relative and static positioning)

– CSS-P was released by W3C in 1997– Completely supported by IE6 and NS7

• Review– Please review absolute and relative

positioning examples from your CSS presentation in week 5!


Moving Elements• If position is set to either absolute or

relative, the element can be moved after it is displayed

• Just change the top and left property values with a script


mover.html• Step 1. Open

Notepad & type header & the code

Type this code

Change top & left properties

Change src to "stars.gif"


mover.html• Step 2. Save

and preview in browser

• Try entering different values for x and y


Element Visibility• The visibility property of an element

controls whether it is displayed• The values are visible and hidden

if (dom.visibility == "visible" dom.visibility = "hidden";else dom.visibility = "visible";

if (dom.visibility == "visible" dom.visibility = "hidden";else dom.visibility = "visible";


showHide.html• Step 1. Open


Type this code

Toggle Visibility property

Notice the airplane picture was used instead of Saturn!


showHide.html• Step 2. Save & preview in a browser


Changing Colors and Fonts

• Colors– Background color is controlled by the

backgroundColor property– Foreground color is controlled by the color

property

• Background color: – The actual parameter this.value works

because at the time of the call, this is a reference to the text box (the element in which the call is made)

– So, this.value is the name of the new color

<input type = "text" size = "10" name = "background“

onchange = "setColor('background', this.value)">

<input type = "text" size = "10" name = "background“

onchange = "setColor('background', this.value)">


dynColors.htm• Step 1. Open


Change background

color

Change text color

Type this code


dynColors.htm• Step 2. Save & preview in a browser


Changing fonts• We can change the font properties of a

link by using the mouseover and mouseout events to trigger a script that makes the changes

onmouseover = "this.style.color = 'blue';

this.style.font = 'italic 16pt Times';"

onmouseout = "this.style.color = 'black';

this.style.font = 'normal 16pt Times';”

onmouseover = "this.style.color = 'blue';

this.style.font = 'italic 16pt Times';"

onmouseout = "this.style.color = 'black';

this.style.font = 'normal 16pt Times';”


dynLink.html

• Step 1. Open Notepad & type header & the code


dynLink.html• Step 2. Save & preview in a browser• Step 3. Mouse over the link to see the new

link style!


Dynamic Content• The content of an HTML element is

addressed with the value property of its associated JavaScript object


dynValue.html• Step 1. Open Notepad & type header & the

code.

Type this code

Create a string array of helper messages


dynValue.html• Step 2. Type the code as shown

Type this code

Pass the helper number when you call for a help message


dynValue.html• Step 3. Save & preview in a browser• Notice as you fill out the form, the message in

the textarea dynamically changes.


Stacking Elements• The z-index attribute determines which

element is in front and which are covered by the front element

• The JavaScript property associated with the– z-index attribute is zIndex– z-index can be changed dynamically (by

changing zIndex)


Stacking Elements• To change stacking order,

– the handler function must change the zIndex property value of the element

– A call to the function from an element sets the zIndex value of the new top element to 10 and the zIndex value of the old top element to 0

– It also sets the current top to the new top


Stacking Elements• An image element can have an onclick

attribute, so images can be clicked to trigger event handlers– Anchors can also trigger event handlers

when they are clicked– The href attribute can be set to call a

JavaScript function by assigning it the call, with 'JAVASCRIPT' attached to the call code

<a href = "JAVASCRIPT:fun()"><a href = "JAVASCRIPT:fun()">


stacking.html• Step 1. Open Notepad & type header & the

code

Type this code


stacking.html• Step 2. Type the code

Type this code


stacking.html• Step 3. Save & preview in a browser

The image is literally covering the other two

images because it’s larger than the other two

in this example!

Try modifying this page with three of your favorite graphics!


stacking.html• If you were to use the original graphics,

this is what you should see:


stacking.html• After clicking on the second image


stacking.html• Sfter clicking on the bottom image


Locating the Mouse Cursor

• The coordinates of the element that caused an event are available in the clientX and clientY properties of the event object– These are relative to upper left corner of

the browser display window– screenX and screenY are relative to the

upper left corner of the whole client screen– If we want to locate the mouse cursor when

the mouse button is clicked, we can use the click event


where.html• Step 1. Open

Notepad & type the code

Type this code

Client Area Coordinates

Screen Coordinates


where.html• Step 2. Save &

preview in a browser

• Click on the upper right corner, just outside of the image to view the coordinates.


Reacting to a Mouse Click

• A mouse click can be used to trigger an action, no matter where the mouse cursor is in the display– Use event handlers for onmousedown and

onmouseup that change the visibility attribute of the message


anywhere.html


Type this code

By putting the code in the body element it applies to the whole

document!


anywhere.html• Step 2. Save & preview in a browser• Note that this doesn’t work IE!


Slow Movement of Elements

• To animate an element, it must be moved by small amounts, many times, in rapid succession

• JavaScript has 2 ways to do this, but we cover just one:

setTimeout("fun()", n)setTimeout("fun()", n)



• Move a text element from its initial– position (100, 100) to a new position (300,

300)– Use the onload attribute of the body

element to initialize the position of the element

– Use a move function to change the top and left attributes by one pixel in the direction of the destination

• Problem: – coordinate properties are stored as strings, – which include the units ("150px")



• Another problem: – We need to use some HTML special

characters (‘<‘ and ‘--’)• XML parsers may remove all comments• Put the script in a CDATA section• Put JavaScript in separate file

– These are problems of validation only– Both IE6 and NS7 deal correctly with

comments


moveText.html


Type this code

Use an external JS file


moveText.html• Step 2. Create the external JS file

Type this code


moveText.html• Step 3. Create the

external JS file

Type this code


moveText.html• Step 4. Save & preview in a browser


Dragging and Dropping• We can use mousedown, mousemove,

and mouseup events to grab, drag, and drop– We know how to move an element - just

change its left and top properties

• Magnetic poetry– The DOM 2 event model is required (the

Event object and its property, currentTarget)

– We use both DOM 0 and DOM 2 models (DOM 0 to call the mousedown handler, grabber)


How to Drag & Drop Elements

• Drag and drop requires 3 processes:1. Get the dom of the element to be moved when

the mouse button is pressed down (onmousedown) while the mouse cursor is over the element to be moved• We can get the DOM of the element on which an event

occurred with the currentTarget property of the event object

2. Move the element by changing its top and left properties of the element as the mouse cursor is moved (onmousemove)• Compute the distance of each move as the difference

between the current position (the left and top values) and the mouse click position (clientX and clientY)

3. Dropping the element when the mouse button is released by undefining the dom used to carry out the move


dragNDrop.html

• Step 1. Open Notepad & type header & the code as shown on page 258 – 261.

• Step 2. Save & preview in a browser– This will not

work with IE6!


Third Party DHTML Scripts

• There are many third party JavaScripts and DHTML snippets that you can use in your web pages to create animation, dynamic menus, and dynamic content. – It’s important to look at them to see how

they work on various platforms. – Some are royalty free, but some require

you to keep the copyright information intact and that you can’t modify the code.

– Always respect the copyright and rules!


Expectations• Students should be able to modify the

attributes of the elements dynamically using CSS and JavaScript (DHTML). For example:– You should describe what the attributes are

used for, and their names and values are. – You should be able to create hyperlinks that

change text properties when users mouse over them. This is commonly used to create menu effects.

– You need to describe the steps to stack elements, hide and unhide elements, and to move elements.


Now you are all ready to start building interactive web

applications!

If you need more help, post your questions in the weekly

Q & A discussion forum.

Ready, Set, Go!

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© Park University, 2006 Creating an Interactive Web Page with DHTML and JavaScript Park University.

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