JavaScript DOM Manipulations

JavaScript
DOM Manipulations and Events

Slides By: Ynon Perek

Fine me at: http://ynonperek.com

Friday, April 12, 13

The Task
Read text Make web
<BODY BGCOLOR='#FFFFFF' style="overflow:hidden;"
LEFTMARGIN=0 MARGINWIDTH=0 TOPMARGIN=0
MARGINHEIGHT=0 CLASS="text" onload="DisplayAD();"
onresize="if(typeof DZresize == 'function'){DZresize();};if(typeof
dcOnResize == 'function'){dcOnResize();};if(typeof
disYnetAdColOnResize == 'function'){disYnetAdColOnResize();};"
lang=he><div id='divRedAlert' style='display:none;'></div><iframe
id=frmRedAlert name=frmRedAlert frameborder=0 width=0 height=0
MARGINHEIGHT=0 MARGINWIDTH=0 src='/Ext/App/RedAlert/
CdaRedAlert_iframe/0,12639,84-234-208-20,00.html'></iframe><div
id='ads.ozen' style='position:absolute;z-index:2;left:0;top:0;'></div><div
id='ads.elvisR.1' style='position:absolute;z-index:2;right:0;top:0;'></
div><div id=mainCont style="overflow:hidden; width:100%; height:100%;"
align=center ><div id='mainSpacer' style='overflow:auto;height:
100%'><script>
<style>A.brightgrey:link{color:#7d7f7e}
A.brightgrey:visited{color:#7d7f7e}A.brightgrey:active{color:#7d7f7e}
A.brightgrey:hover{color:#f00}A.upnvl{color:#7d7f80}
A.upnvl:visited{color:#7d7f80}A.upnvl:hover{color:#f00}
A.btnvl{color:#7f90b0}A.btnvl:visited{color:#7f90b0}
A.btnvl:hover{color:#f00}</style><table id=tbl_logos cellspacing=0 cetd
width='46' align='left' style='line-height:12px;'><a href='http://
www.ynetnews.com/home/0,7340,L-3083,00.html' class='text11
btnvl'>English</a></td></tr></table></div></td><td width=11> </
td><td width=2 bgcolor=black></td><td width=11> </td><td
width=132 valign=top style='direction: rtl;' class='ghci3' ><div
id=divMainLogo style='margin-top:1px;'></div></td><td width=11><div
style='width:11px;'></div></td><TD WIDTH=194 align=right dir=rtl
VALIGN=top class='ghciTopStoryMain1' ><div dir=ltr style='height:
38px;overflow:hidden;'><IMG SRC='/Common/Files/Images/Date/12.gif'
alt="12/04/2013 11:20"><IMG SRC='/Common/Files/Images/D...


How Browsers Render

• Each browser has a Rendering Engine
• Rendering Engine takes an HTML text
and produces a DOM tree


Rendering Engines
Engine Browser Developer

Blink Google Chrome Google

Gecko Mozilla Firefox Mozilla

Trident IE Microsoft

Apple, KDE, Nokia,
Webkit Apple Safari
Others


How Browsers Work
Parse HTML to make DOM Tree

Build Render Tree from CSS

Layout Elements

Paint


What’s a DOM Tree

<html>
<body>
<p>
Hello World
</p>
<div>
<img src="example.png"/>
</div>
</body>
</html>


Rendering DOM Tree


Rendering DOM Tree

• A Render tree is derived from DOM
tree
• It’s not a 1-1 relation


Browser Flow

• Read page as text
• Create DOM tree
• Create Render tree
• Paint


Enter JavaScript

• Read page as text
• Create DOM tree JavaScript
Manipulates the
• Create Render tree
data
• Paint


Enter JavaScript

• JavaScript alters page load

• JavaScript alters DOM Tree
• JavaScript creates interactivity through
events handling


JavaScript and DOM
<!DOCTYPE html>
<html>
<head>
<title></title>
</head>
<body> A <script> element is
<script>
var x = 5; executed in place
var y = 3;
console.log('Hello From JS');
</script>
<p>This is just some text</p>
</body>
</html>


Q&A
Browser Page Rendering


Interactive Apps

• Browser is a programming platform
• A web application is interactive


Interactivity

• Browser itself is interactive
• In addition: A web page is interactive
• Demo


Browser Events Loop

Event Queue

click


Event Loop

Wait for Events

Handle Events


Event Handling

DOM Node

+ Event Handler (code)

Event


Code Outline

• From HTML:
• <a on...=”handleEvent()”>


Code Outline
• But this can get messy
<a href="#" onclick="doclick"
onblur="doblur"
onchange="dochange"
ondblclick="dodblclick"
onmousemove="domove"
onmouseover="doover">
Too many events</a>


Code Outline

• From JS
• Get a DOM node
• Bind event to code


Getting DOM Nodes

• getElementById(...)
• getElementsByTagName(...)
• querySelector(...) - IE8 and up


Browser Events

• All browsers use:
node.onevent = ...
• IE uses:
node.attachEvent(...)
• Other browsers use
node.addEventListener(...)


Demo: Events

• Write a simple page that shows alert as
a response to click event
• Modify to change text of element


Using the Event Object
• Event object includes info on the event
• Print it to console for inspection

<button>Click Me</button>

<script>
var btn = document.getElementsByTagName('button')[0];
btn.onclick = function(e) {
if ( ! e ) e = window.event;

console.dir( e );
};
</script>


Capturing vs. Bubbling

| | /
---------------| |----------------- ---------------| |-----------------
| element1 | | | | element1 | | |
| -----------| |----------- | | -----------| |----------- |
| |element2 / | | | |element2 | | | |
| ------------------------- | | ------------------------- |
| Event CAPTURING | | Event BUBBLING |
----------------------------------- -----------------------------------



| | /
---------------| |----------------- ---------------| |-----------------
| element1 | | | | element1 | | |
| -----------| |----------- | | -----------| |----------- |
| |element2 / | | | |element2 | | | |
| ------------------------- | | ------------------------- |
| Event CAPTURING | | Event BUBBLING |
----------------------------------- -----------------------------------

Netscape Microsoft



| | /
-----------------| |--| |-----------------
| element1 | | | | |
| -------------| |--| |----------- |
| |element2 / | | | |
| -------------------------------- |
| W3C event model |
------------------------------------------



• node.addEventListener takes a third
parameter
• true means capturing
• false means bubbling
• defaults to false


Demo

• Capture all click events using
document.onclick = ...


Usages

• Default event handlers
• Dynamic event handlers


Double Handlers

element1.onclick =
Element2 doSomething;
Element1 element2.onclick =
doSomething;


Double Handlers
function doSomething(e) {
if ( ! e ) e = window.event;
Element2
// this refers to
Element1 // the current element

// for inner event:
// this = element2

// for outer event:
// this = element1
}


Event Types
Interface Events Mouse Events Form Events

load, unload click, dblclick submit

mousedown, mouseup,
resize, scroll, reset
mousemove

focus, blur mouseover, mouseout


Default Action

• Some events also have a “default”
action
• For example: A link will take you to
another page by default


Default Action

• Possible to prevent
• return false from handler
• Demo


Q&A
Handling Events


Events Lab

• Implement 5 duplicated input boxes
• Each input box should have the same
text
• Change one -> all change automatically


Events Lab


Altering Page Load

• Change Document
• Change DOM Tree
• Change Render Tree


Change Document

• (Don’t) use document.write to change
the document as it’s being loaded
• Considered bad practice


Change Document
<!DOCTYPE html>
<html>
<head>
<title></title>
</head>
<body>
<script>
document.write('<h1>Hello World</h1>');
</script>
<p>This is just some text</p>
</body>
</html>


Change Document
1. Browser starts to
create DOM tree

body

2. Finds a script tag.
script Stops to execute


Change Document

body

3. script added <h1>
script h1 element to document


Change Document

body

script h1 p

4. browser can continue
to create the <p>


Avoiding document.write

• Can insert invalid content
• Clobbers DOM if called after reading
the document


Friendlier Ways

• Get a DOM node
• Change it using DOM API


Finding
DOM
Nodes


DOM Traversal
<body> body
<div>
<h1>Header</h1>
<p>
<img src="..." /> #text #div #text
Paragraph text
<a
href="#">google</a> #text #text #h1 #text #p
</p>
</div>
</body>


DOM Traversal
• n.childNodes[]
• n.firstChild
• n.lastChild
• n.nextSibling
• n.parentNode
• n.previousSibling


The (Past) Future

• document.querySelector takes any CSS
selector and fetches DOM element
• Supported in IE8 and later


DOM API

• Allows
• Getting info on elements
• Changing element attributes
• Creating new elements
• Setting elements style


DOM API
• Use x.nodeName to get the tag name

if ( this.nodeName === 'INPUT' ){
// handle input element
}


DOM API

• Use x.nodeValue to get/set the node
value

a.firstChild.nodeValue = 'Go to google';


DOM API
• Use getAttribute / setAttribute to
change element attributes

a.setAttribute('href',
'http://www.google.com');


Creating New Elements
• Create elements and text nodes using
document
• Later you can add them to the DOM

document.createElement('P');

document.createTextNode('Hello
World');


Creating New Elements
• Insert new nodes by manipulating
existing
// append y to x
x.appendChild(y)

// insert y to x before z
x.insertBefore(y,z)

// remove y from x
x.removeChild(y)

// replace y with z
x.replaceChild(y,z)


Change Style
• Use .style property to set an element
style
• Note style keys are almost like CSS
property names

p.style.backgroundColor = 'blue';


DOM Lab
• Given the HTML at:
http://jsbin.com/ecitag/1/edit
• Use JavaScript to:
• write your name in the ﬁrst <li> item
of the second list
• Change the H3 to H4
• Set all links to point to google.com


DOM Lab

• Create a Money Converter calculator
• Support 3 currencies


JavaScript DOM Manipulations

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