CD-561Appendix F . Examples from Parts III and IV You can also click other places on the page. For example, if you click to the right of the button, you will be clicking the FORM element. Event propagation and processing adjusts accordingly. Similarly, if you click the header text, the only event listeners that see the event are in the document and BODY levels. eventPhase NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility Example See Listing 29-20 earlier in this chapter for an example of how you can use a switch construction to branch function processing based on the event phase of the current event object. relatedTarget NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility Example Listing 29-21 provides an example of how the relatedTargetproperty can reveal the life of the cursor action before and after it rolls into an element. When you roll the cursor to the center box (a table cell), its onMouseOver event handler displays the text from the table cell from which the cursor arrived (the nodeValue of the text node inside the table cell). If the cursor comes in from one of the corners (not easy to do), a different message is displayed. (NN6) eventObject.relatedTarget
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CD-560 Part VI . Appendixes Listing 29-20: currentTarget and eventPhase Properties

currentTarget and eventPhase Properties

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(NN6) eventObject.currentTarget
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CD-559Appendix F . Examples from Parts III and IV

Click on the button and in the DIV/image to see the coordinate values for the event object.

NN6 Mouse Event Coordinates:
target:
clientX, clientY:		…With scrolling:
layerX, layerY:
pageX, pageY:		Within Element:
screenX, screenY:

currentTarget NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility Example Listing 29-20 shows the power of the currentTargetproperty in revealing the element that is processing an event during event propagation. Similar to the code in Listing 29-7, this example is made simpler because it lets the event object s properties do more of the work to reveal the identity of each element that processes the event. Event listeners assigned for various propagation modes are assigned to a variety of nodes in the document. After you click the button, each listener in the propagation chain fires in sequence. The alert dialog shows which node is processing the event. And, as in Listing 29-7, the eventPhase property is used to help display the propagation mode in force at the time the event is processed by each node. (NN6) eventObject.currentTarget
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CD-558 Part VI . Appendixes Example You can see the effects of the coordinate systems and associated NN6 properties with the page in Listing 29-19. You can view coordinate values for all four measuring systems, as well as some calculated value. Two clickable objects are provided so that you can see the differences between an object not in any layer and an object residing within a layer (although anything you see is clickable, including text nodes). One of the calculated fields applies window scrolling values to the client coordinates. But, as you will see, these calculated values are the same as the more convenient page coordinates. The other calculated field shows the coordinates relative to the rectangular space of the target element. Notice in the code that if the nodeType of the target indicates a text node, that node s parent node (an element) is used for the calculation. Listing 29-19: NN6 Event Coordinate Properties

X and Y Event Properties (NN6+)

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(NN6) eventObject.clientX
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CD-557Appendix F . Examples from Parts III and IV Here are some specific tasks to try with the page to examine key codes (if you are not using a browser set for English and a Latin-based keyboard, your results may vary): 1. Enter a lowercase letter a . Notice how the onKeyPress event handler shows the charCode to be 97, which is the Unicode (and ASCII) value for the first of the lowercase letters of the Latin alphabet. But the other two event types record just the key s code: 65. 2. Type an uppercase A via the Shift key. If you watch closely, you see that the Shift key, itself, generates the key code 16 for the onKeyDown and onKeyUp events. But the character key then shows the value 65 for all three events (until you release the Shift key), because the ASCII value of the uppercase letter happens to match the keyboard key code for that letter. 3. Press and release the Down Arrow key (be sure the cursor still flashes in the TEXTAREA, because that s where the keyboard events are being monitored). As a non-character key, all three events stuff a value into the keyCode property, but zero into charCode. The keyCode value for this key is 40. 4. Poke around with other non-character keys. Some may produce dialog boxes or menus, but their key codes are recorded nonetheless. clientX clientY layerX layerY pageX pageY screenX screenY NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility (NN6) eventObject.clientX
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CD-556 Part VI . Appendixes Example Listing 29-18 provides a play area to view the charCode and keyCodeproperties for all three keyboard events while you type into a TEXTAREA. You can use this later as an authoring tool to grab the precise codes for keyboard keys you may not be familiar with. Listing 29-18: Displaying charCode and keyCode Property Values

charCode and keyCode Properties

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Event	event.charCode	event.keyCode
onKeyDown:
onKeyPress:
onKeyUp:

(NN6) eventObject.charCode
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CD-555Appendix F . Examples from Parts III and IV Lorem ipsum dolor sit amet, consectetaur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim adminim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.

type NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility Example Use The Evaluator (Chapter 13) to see values returned by the type property. Enter the following object name into the bottom text box and press Enter/Return: event If necessary, scroll the Results box to view the type property, which should read keypress. Now click the List Properties button. The type changes to click. The reason for these types is that the eventobject whose properties are being shown here is the event that triggers the function to show the properties. From the text box, an onKeyPress event handler triggers that process; from the button, an onClick event handler does the job. NN6+ event Object charCode keyCode NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility (NN6) eventObject.charCode
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CD-554 Part VI . Appendixes three SPAN elements in the paragraph the style sheet rule for that class is modified so that all items share the same color. Your scripts can do even more in the way of filtering objects that arrive at the functions to perform special operations on certain objects or groups of objects. Notice that the scripts don t have to know anything about the objects on the page to address each clicked one individually. That s because the srcElement property provides all of the specificity needed for acting on the target element. Listing 29-17: Using the srcElement property

srcElement Property

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One event handler…

• Can
• Cover
• Many
• Objects

(IE) event.srcElement
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CD-553Appendix F . Examples from Parts III and IV But the character key then shows the value 65 for all three events, because the ASCII value of the uppercase letter happens to match the keyboard key code for that letter. 3. Press and release the Down Arrow key (be sure the cursor still flashes in the TEXTAREA, because that s where the keyboard events are being monitored). As a non-character key, it does not fire an onKeyPress event. But it does fire the other events, and assigns 40 as the code for this key. 4. Poke around with other non-character keys. Some may produce dialog boxes or menus, but their key codes are recorded nonetheless. Note that not all keys on a Macintosh keyboard register with IE/Mac. returnValue NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility Example You can find several examples of the returnValueproperty at work in Chapter 15. Look at Listings 15-30, 33, 36, 37, 38, and 45. Moreover, many of the other examples in that chapter can substitute the returnValueproperty way of cancelling the default action if the scripts were to be run exclusively on IE4+. srcElement NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility Example As a simplified demonstration of the power of the srcElement property, Listing 29-17 has but two event handlers defined for the BODY element, each invoking a single function. The idea is that the onMouseDown and onMouseUp events will bubble up from whatever their targets are, and the event handler functions will find out which element is the target and modify the color style of that element. An extra flair is added to the script in that each function also checks the className property of the target element. If the className is bold a class name shared by (IE) event.srcElement
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CD-552 Part VI . Appendixes Listing 29-16 (continued)

keyCode Property

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Event	event.keyCode
onKeyDown:
onKeyPress:
onKeyUp:

The following are some specific tasks to try with the page to examine key codes (if you are not using a browser set for English and a Latin-based keyboard, your results may vary): 1. Enter a lowercase letter a . Notice how the onKeyPress event handler shows the code to be 97, which is the Unicode (and ASCII) value for the first of the lowercase letters of the Latin alphabet. But the other two events record just the key s code: 65. 2. Type an uppercase A via the Shift key. If you watch closely, you see that the Shift key, itself, generates the code 16 for the onKeyDown and onKeyUp events. (IE) event.keyCode
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