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

© Park University, 2006 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

© Park University, 2006 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

© Park University, 2006 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!

© Park University, 2006 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

© Park University, 2006 mover.html Step 1. Open Notepad & type header & the code Type this code Change top & left properties Change src to "stars.gif"

© Park University, 2006 mover.html Step 2. Save and preview in browser Try entering different values for x and y

© Park University, 2006 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";

© Park University, 2006 showHide.html Step 1. Open Notepad & type header & the code Type this code Toggle Visibility property Notice the airplane picture was used instead of Saturn!

© Park University, 2006 showHide.html Step 2. Save & preview in a browser

© Park University, 2006 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

© Park University, 2006 dynColors.htm Step 1. Open Notepad & type header & the code Change background color Change text color Type this code

© Park University, 2006 dynColors.htm Step 2. Save & preview in a browser

© Park University, 2006 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';”

© Park University, 2006 dynLink.html Step 1. Open Notepad & type header & the code

© Park University, 2006 dynLink.html Step 2. Save & preview in a browser Step 3. Mouse over the link to see the new link style!

© Park University, 2006 Dynamic Content The content of an HTML element is addressed with the value property of its associated JavaScript object

© Park University, 2006 dynValue.html Step 1. Open Notepad & type header & the code. Type this code Create a string array of helper messages

© Park University, 2006 dynValue.html Step 2. Type the code as shown Type this code Pass the helper number when you call for a help message

© Park University, 2006 dynValue.html Step 3. Save & preview in a browser Notice as you fill out the form, the message in the textarea dynamically changes.

© Park University, 2006 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)

© Park University, 2006 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

© Park University, 2006 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

© Park University, 2006 stacking.html Step 1. Open Notepad & type header & the code Type this code

© Park University, 2006 stacking.html Step 2. Type the code Type this code

© Park University, 2006 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!

© Park University, 2006 stacking.html If you were to use the original graphics, this is what you should see:

© Park University, 2006 stacking.html After clicking on the second image

© Park University, 2006 stacking.html Sfter clicking on the bottom image

© Park University, 2006 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

© Park University, 2006 where.html Step 1. Open Notepad & type the code Type this code Client Area Coordinates Screen Coordinates

© Park University, 2006 where.html Step 2. Save & preview in a browser Click on the upper right corner, just outside of the image to view the coordinates.

© Park University, 2006 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

© Park University, 2006 anywhere.html Step 1. Open Notepad & type header & the code Type this code By putting the code in the body element it applies to the whole document!

© Park University, 2006 anywhere.html Step 2. Save & preview in a browser Note that this doesn’t work IE!

© Park University, 2006 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)

© Park University, 2006 Slow Movement of Elements 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")

© Park University, 2006 Slow Movement of Elements 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

© Park University, 2006 moveText.html Step 1. Open Notepad & type header & the code Type this code Use an external JS file

© Park University, 2006 moveText.html Step 2. Create the external JS file Type this code

© Park University, 2006 moveText.html Step 3. Create the external JS file Type this code

© Park University, 2006 moveText.html Step 4. Save & preview in a browser

© Park University, 2006 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)

© Park University, 2006 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

© Park University, 2006 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!

© Park University, 2006 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!

© Park University, 2006 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.

© Park University, 2006 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!