1. Document Object Model

2. Javascript and the DOM
Originally, the Document Object Model (DOM) and Javascript were tightly bound
Each major browser line (IE and Netscape) had their own overlapping DOM implementation
There's also some jargon issues, eg. DHTML…
Now, the DOM is a separate standard, and can be manipulated by other languages (eg Java, server side javascript, python, etc)
Browsers still differ in what parts of the standard they support, but things are much better now

3. Review: DOM Structure Objects are in a hierarchy
window
* location
* frames
* history
* navigator
* event
* screen
* document
o links
o anchors
o images
o filters
o forms
o applets
o embeds
o plug-ins
o frames
o scripts
o all
o selection
o stylesheets
o body
Objects are in a hierarchy
The window is the parent for a given web page
Document is the child with the objects that are most commonly manipulated
table from:

4. DOM Tree The usual parent/child relationship between node
Like any other tree, you can walk this
diagram from

5. Referencing Objects
Objects can be referenced
by their id or name (this is the easiest way, but you need to make sure a name is unique in the hierarchy)
by their numerical position in the hierarchy, by walking the array that contains them
by their relation to parent, child, or sibling (parentNode, previousSibling, nextSibling, firstChild, lastChild or the childNodes array

6. A div example the div is an element with an id of mydiv
It contains a text element, which can be referenced by childNodes[0] (childNode being an array of all childen of a node
So the text in the div is not a value of the div, but rather the value of the first (and only) childNode of the div
<div id="mydiv">
This is some simple html to display
</div>

7. Zen Garden Example 1 A loop of code to list the links….
for (var i = 0; i < document.links.length; i++) {
document.write("<b>Link number " + i + " has these properties:</b><br/>");
document.write("<i>nodeName is</i> " + document.links[i].nodeName + "<br/>");
document.write("<i>nodeType is</i> " + document.links[i].nodeType + "<br/>");
document.write("<i>parentNode.nodeValue is</i> " document.links[i].parentNode.nodeValue + "<br/>");
document.write("<i>firstChild is</i> " + document.links[i].firstChild + "<br/>");
document.write("<i>firstChild.nodeValue is</i> " document.links[i].firstChild.nodeValue + "<br/>");
document.write("<i>href is</i> " + document.links[i].href + "<br/>"); }

8. Zen Garden Example 2
Same as example one, but with another loop to look for all span tags….

9. Zen Garden Example 2
I added a little javascript to the sample file from zen garden
This will search for a given tag using the getElementsByTagName() method
The result of this method is an array, and we can walk that array and then write out different properties and values for the elements found by getElementsByTagName()
There's also a getElementsById() method

10. Zen Garden Example 2 var look_for="span";
document.write("<p>Looking for " + look_for + " tags</p>");
var x=document.getElementsByTagName(look_for);
for (var i = 0; i < x.length; i++) {
document.write("<b>Tag " + look_for + " number " + i + " has these properties:</b><br/>");
document.write("<i>nodeName is</i> " + x[i].nodeName + "<br/>");
document.write("<i>nodeValue is</i> " + x[i].nodeValue + "<br/>");
document.write("<i>nodeType is</i> " + x[i].nodeType + "<br/>");
document.write("<i>id is</i> " + x[i].id + "<br/>");
document.write("<i>name is</i> " + x[i].name + "<br/>");
document.write("<i>parentNode is</i> " + x[i].parentNode + "<br/>");
document.write("<i>parentNode.nodeValue is</i> " + x[i].parentNode.nodeValue + "<br/>");
document.write("<i>firstChild is</i> " + x[i].firstChild + "<br/>");
document.write("<i>firstChild.nodeValue is</i> " + x[i].firstChild.nodeValue + "<br/>"); }

11. Learning The DOM The only way is to read and try things out
Build a test document, with things you've learned
Gecko_test.html is an example adapted from the mozilla site….

12. Gecko Test version 1 Notice the use of eval
function setBodyAttr(attr,value) {
// eval causes a string to be executed
eval('document.body.' + attr + '="' + value + '"');
document.main_form.object_manipulated.value='document.body.'
+ attr + '="' + value + '"'; }
gecko_test01.html

13. Gecko Test version 1 And a select
<select onChange="setBodyAttr('text',
this.options[this.selectedIndex].value);">
<option value="blue">blue
<option value="green">green
<option value="black">black
<option value="darkblue">darkblue
<option value="white">white …
</select>
gecko_test01.html

14. Gecko Test version 1
What's wrong with this? (hint: I'm violating a basic rule of coding…)
gecko_test01.html

15. Gecko Test version 2
Setting a variable for the options in select (why backslashes at the EOLs?):
var select_string='<option value="blue">blue</option>\
<option value="green">green</option>\
<option value="black">black</option>\
<option value="darkblue">darkblue</option>\
<option value="white">white</option>\
<option value="0xFF5555">0xFF5555</option>';
gecko_test02.html

16. Gecko Test version 2 And now, I can call that list with a write
How could I further refine this?
<select onchange=
"setBodyAttr('bgColor', this.options[this.selectedIndex].value);">
<script type="application/x-javascript">
document.write(select_string);
</script></select></p>
gecko_test02.html

17. Manipulating Objects As said, it's easiest to reference objects by id
To do this easily, use getElementById(), which returns the element with the given id
For example, if you want to find a div with the id of "my_cool_div", use getElementById("my_cool_div")
Keep in mind that it's the element itself that's returned, not any particular property

18. Using divs Div properties can be dynamically manipulated
You can use this to make menus more dynamic

19. colors: The first version
The basic div:
<div id="item1" class="content"
onMouseOver="changeColor('item1', '#fdd');"
onMouseOut="changeColor('item1', '#cff');">
<a href="
</div>
<br>
colors01.html

20. colors: The First Version
And a function (notice the alert):
<script>
function changeColor(item, color) {
document.getElementById(item).style.backgroundColor
=color;
//alert(document.getElementById(item).childNodes[1]);
document.getElementById(item).childNodes[1].style.backgroundColor }
</script>
colors01.html

21. In Action
colors01.html
What's wrong with this? What would be better?

22. Version 2 The div structure, sans link:
<div id="item1" class="content"
onMouseOver="changeColor('item1', change_color);"
onMouseOut="changeColor('item1', start_color);"
onClick="document.location='
>
UNC
</div>
colors02.html

23. Version 2 And the function, with some vars <script>
function changeColor(item, color) {
document.getElementById(item).style.backgroundColor=color; }
var start_color="#cff";
var change_color="#fdd";
</script>
colors02.html

24. Version2
Much cleaner
div clickable means no issues with color of link, but sacrifices visited link color (how could that be fixed?)
Use of variables for colors mean it's much easier to change them (but this could be made much easier with php in the background…)

25. innerHTML
innerHTML is a property of any document element that contains all of the html source and text within that element
This is not a standard property, but widely supported--it's the old school way to manipulate web pages
Much easier than building actual dom subtrees, so it's a good place to start
Very important--innerHTML treats everything as a string, not as DOM objects (that's one reason it's not part of the DOM standard)

26. Using These….
You can reference any named element with getElementById()
You can read from or write to that element with innerHTML
For example: getElementById("mydiv").innerHTML ="new text string";

27. A Simple DOM example <div id="mydiv"> <p>
This some <i>simple</i> html to display
</p>
</div>
<form id="myform">
<input type="button" value="Alert innerHTML of mydiv"
onclick="
alert(getElementById('mydiv').innerHTML)
" />
</form>
simple_dom_example.html

28. Manipulating Visibility
You can manipulate the visibility of objects, this from
The first part displays an element if it's hidden…
function changeDisplayState (id) {
trigger=document.getElementById("showhide");
target_element=document.getElementById(id);
if (target_element.style.display == 'none'
|| target_element.style.display == "")
target_element.style.display = 'block';
trigger.innerHTML = 'Hide example'; } …
31_dhtml_example.html

29. Manipulating Visibility
And the second hides the same element if it's visible …
else {
target_element.style.display = 'none';
trigger.innerHTML = 'Show example'; }
31_dhtml_example.html

30. Controlling the back end
And you can enable or disable functionality, for example, you can disable links dynamically…
function killAll() {
var stuff = document.getElementsByTagName("A");
for (var i=0; i<stuff.length; i++)
stuff[i].onclick=function()
return false ; }
source from Mike Harrison via chugalug.org 35_disable_links.html

31. Controlling the back end
…and reenable them…
function resurrectAll() {
var stuff = document.getElementsByTagName("A");
for (var i=0; i<stuff.length; i++)
stuff[i].onclick=function()
return true ; }
source from Mike Harrison via chugalug.org 35_disable_links.html

32. Getting fancier
check out Nifty Corners Cube:
And zoom:

33. What else can you do?
Ant

34. Getting Started with Ajax
Jesse James Garrett coined the term, Asynchronous Javascript And XML
It's not a language or program, but rather an approach

35. Garrett's take on what Ajax is
Standards-based presentation using XHTML and CSS
Dynamic display and interaction using the Document Object Model
Data interchange and manipulation using XML and XSLT
Asynchronous data retrieval using XMLHttpRequest
And JavaScript binding everything together

36. What Ajax is not An acronym
A monolith or unified technology (it is rather an approach based on a number of disparate technologies)
A standard (and it's not likely to become one, although it will influence standards, since it's really just an approach)
A product (although you can buy a lot of it these days--but most of that are really frameworks)

37. Ok, but what IS Ajax? When you load a web page and then
Use the XMLHttpRequest object to get some more data, and then
Use Javascript to change some of the data on your web page (but not all of it, and not by reloading the page), then
What you're doing is Ajax

38. Ajax Model
Ajax inserts a chunk of code in the browser that handles server queries for small chunks of data used to update a document
diagram from

39. But remember…
Javascript has no concept of I/O, nor can it access sockets
But Netscape/Mozilla and MS both worked out an object in the browser that can submit data requests via the web
In MS, this is done via ActiveX, via the Microsoft.XMLHTTP object
In Gecko, it's the XMLHttpRequest() object, and that's what we'll play with

40. Objects and Events
Remember, Javascript and the DOM are OOP, so objects have properties, with values, and can receive messages, based on events, and send messages via methods
In most of the examples so far, the user is the one that causes an event to occur--eg. the nav buttons in the slideshow call functions based on an event initiated by a carbon unit
Other events don't require human interaction--these type of events are called "listeners"…
You can create your own listeners if you need to

41. XMLHttpRequest Object
An object that can load web resources from within javascript
So you create an instance of this object
Call the open method from that object with a url and a method to use (GET or POST)
It makes the HTTP request, and as it does so, one of it's properties cycles through the states of the HTTP request
You watch that, and when the request is complete, you can get the data that was retrieved

42. XMLHttpRequest Methods
abort()
getAllResponseHeaders()
getResponseHeader(header)
open(method, url): method is POST, GET, or PUT)
send(body): body is the content of a post….
setRequestHeader(header, value)

43. XMLHttpRequest Properties
onreadystatechange: sets a method to be called on any state change, eg. a listener
readState:
Uninitated
Loading
Loaded
Interactive
Complete
responseText: server response as a string
responseXML: server response as xml
status: as an HTTP code, eg 404
statusText: the accompanying text

44. An Example…

45. 00_ajax_demo.html: i function makeRequest(url) {
var http_request = false;
if (window.XMLHttpRequest) { // Mozilla, Safari, ...
http_request = new XMLHttpRequest();
if (http_request.overrideMimeType) {
http_request.overrideMimeType('text/xml'); }
if (!http_request) {
alert('Giving up :( Cannot create an XMLHTTP instance');
return false;
http_request.onreadystatechange = function() {
alertContents(http_request);
http_request.open('GET', url, true);
http_request.send(null);
00_ajax_demo.html: i

46. function alertContents(http_request) {
if (http_request.readyState == 4) {
if (http_request.status == 200) {
alert(http_request.responseText);
} else {
alert('There was a problem with the request.'); }
00_ajax_demo.html: i

47. Security Concerns At first, this kind of call wasn't restricted
But that meant that if one could inject javascript into a web page, eg. via a comment form, one could pull live data into a users brower, and thus escape the sandbox
So now, this method is generally restricted to the same named server…

48. Some Examples
00_ajax_demo.html: in this one, I'm just pulling some data from the server, and stuffing the results into an alert

49. Jah and Ajah and Ahah: HA!
After Garret's coining of the term ajax, several people independently presented similar systems--this is to be expected, since XMLHttpRequest has been around a while
Most of these used the same basic approach to pull html or other data types than xml, or didn't use the dom specification

50. Jah Jah is the work of Kevin Marks
Jah relies on two simple functions, one to open the request, and the other to change the data
Instead of manipulating the dom directly, jah uses the innerHTML property to manipulate the page
See: for an example (or the copy I've got in the lessons folder)

51. Jah Function function jah(url,target) {
// native XMLHttpRequest object
document.getElementById(target).innerHTML = 'sending...';
if (window.XMLHttpRequest) {
req = new XMLHttpRequest();
req.onreadystatechange = function() {jahDone(target);};
req.open("GET", url, true);
req.send(null);
// IE/Windows ActiveX version
} else if (window.ActiveXObject) {
req = new ActiveXObject("Microsoft.XMLHTTP");
if (req) {
req.send(); }

52. Jahdone Function function jahDone(target) { // only if req is "loaded"
if (req.readyState == 4) {
// only if "OK"
if (req.status == 200) {
results = req.responseText;
document.getElementById(target).innerHTML = results;
} else {
document.getElementById(target).innerHTML="jah error:\n" +
req.statusText; }

53. Jah in Action

54. So how can we use this? Make live insertions into a page via the DOM
We'll do more of this next week