The document provides an overview of the Document Object Model (DOM) and how JavaScript can be used to manipulate the DOM. It discusses how the DOM used to be browser-specific but is now a standard that can be manipulated by various languages. It provides examples of DOM tree structure, referencing DOM objects by ID, and manipulating DOM properties like innerHTML and visibility. The document is intended as a tutorial for learning the DOM and JavaScript DOM manipulation.

1. Document Object Model

2. Back to the DOM…

3. 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

4. Review: DOM Structure
 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
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
table from: http://www.webmonkey.com/webmonkey/97/32/index1a.html?tw=authoring

5. DOM Tree
 The usual parent/child relationship between node
 Like any other tree, you can walk this
diagram from http://www.w3schools.com/htmldom/default.asp

6. 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

7. 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"><div id="mydiv">
This is some simple html to displayThis is some simple html to display
</div></div>

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

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

10. 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

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

12. 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….

13. Gecko Test version 1
 Notice the use of eval
function setBodyAttr(attr,value)function setBodyAttr(attr,value)
{{
// eval causes a string to be executed// eval causes a string to be executed
eval('document.body.' + attr + '="' + value + '"');eval('document.body.' + attr + '="' + value + '"');
document.main_form.object_manipulated.value='document.body.'document.main_form.object_manipulated.value='document.body.'
+ attr + '="' + value + '"';+ attr + '="' + value + '"';
}}
gecko_test01.htmlgecko_test01.html

14. Gecko Test version 1
 And a select
<select onChange="setBodyAttr('text',<select onChange="setBodyAttr('text',
this.options[this.selectedIndex].value);">this.options[this.selectedIndex].value);">
<option value="blue">blue<option value="blue">blue
<option value="green">green<option value="green">green
<option value="black">black<option value="black">black
<option value="darkblue">darkblue<option value="darkblue">darkblue
<option value="white">white<option value="white">white
……
</select></select>
gecko_test01.htmlgecko_test01.html

15. Gecko Test version 1
 What's wrong with this? (hint: I'm
violating a basic rule of coding…)
gecko_test01.htmlgecko_test01.html

16. 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>var select_string='<option value="blue">blue</option>
<option value="green">green</option><option value="green">green</option>
<option value="black">black</option><option value="black">black</option>
<option value="darkblue">darkblue</option><option value="darkblue">darkblue</option>
<option value="white">white</option><option value="white">white</option>
<option value="0xFF5555">0xFF5555</option>';<option value="0xFF5555">0xFF5555</option>';
gecko_test02.htmlgecko_test02.html

17. Gecko Test version 2
 And now, I can call that list with a write
 How could I further refine this?
<select onchange=<select onchange=
"setBodyAttr('bgColor', this.options[this.selectedIndex].value);">"setBodyAttr('bgColor', this.options[this.selectedIndex].value);">
<script type="application/x-javascript"><script type="application/x-javascript">
document.write(select_string);document.write(select_string);
</script></select></p></script></select></p>
gecko_test02.htmlgecko_test02.html

18. 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

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

20. colors: The first version
 The basic div:
colors01.htmlcolors01.html
<div id="item1" class="content"<div id="item1" class="content"
onMouseOver="changeColor('item1', '#fdd');"onMouseOver="changeColor('item1', '#fdd');"
onMouseOut="changeColor('item1', '#cff');">onMouseOut="changeColor('item1', '#cff');">
<a href="http://www.unc.edu/">UNC</a><br><a href="http://www.unc.edu/">UNC</a><br>
</div></div>
<br><br>

21. colors: The First Version
 And a function (notice the alert):
<script><script>
function changeColor(item, color)function changeColor(item, color)
{{
document.getElementById(item).style.backgroundColordocument.getElementById(item).style.backgroundColor
=color;=color;
//alert(document.getElementById(item).childNodes[1]);//alert(document.getElementById(item).childNodes[1]);
document.getElementById(item).childNodes[1].style.backgroundColordocument.getElementById(item).childNodes[1].style.backgroundColor
=color;=color;
}}
</script></script>
colors01.htmlcolors01.html

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

23. Version 2
 The div structure, sans link:
colors02.htmlcolors02.html
<div id="item1" class="content"<div id="item1" class="content"
onMouseOver="changeColor('item1', change_color);"onMouseOver="changeColor('item1', change_color);"
onMouseOut="changeColor('item1', start_color);"onMouseOut="changeColor('item1', start_color);"
onClick="document.location='http://www.unc.edu';"onClick="document.location='http://www.unc.edu';"
>>
UNCUNC
</div></div>

24. Version 2
 And the function, with some vars
colors02.htmlcolors02.html
<script><script>
function changeColor(item, color)function changeColor(item, color)
{{
document.getElementById(item).style.backgroundColor=color;document.getElementById(item).style.backgroundColor=color;
}}
var start_color="#cff";var start_color="#cff";
var change_color="#fdd";var change_color="#fdd";
</script></script>

25. 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…)

26. 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)

27. 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";

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

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

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

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

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

33. Getting fancier
 check out Nifty Corners Cube:
http://www.html.it/articoli/niftycube/index.html
 And zoom:
http://valid.tjp.hu/zoom/index_en.html

34. What else can you do?
 Ant

35. 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

36. 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

37. 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)

38. 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

39. 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 http://www.adaptivepath.com/ideas/essays/archives/000385.phpdiagram from http://www.adaptivepath.com/ideas/essays/archives/000385.php

40. 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

41. 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

42. 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

43. 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)

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

45. An Example…

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

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

48. 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…

49. 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

50. 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

51. 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:
http://homepage.mac.com/kevinmarks/staticjah.html
for an example (or the copy I've got in the lessons folder)

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

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

54. Jah in Action

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