159.339 1 DHTML Dynamic Hypertext Markup Language Client-side Programming Lecture

159.339

1

DHTMLDynamic Hypertext Markup Language

Client-side ProgrammingLecture

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Topics for Discussion

What is DHTML?

CSS

Javascript

DOM, Examples

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Dynamic HTML

Cascading style sheets, HTML, DOM and Javascript

159.339DHTML

• Collection of technologies forming dynamic clients– HTML (content)– DOM (data structure)– JavaScript (behaviour)– Cascading Style Sheets (presentation)

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HTML Element

159.339HTML ELEMENT

onblur When an element loses focus

onclick When a mouseclick on an element

ondblclick When a mouse-doubleclick on an element

onfocus When an element gets focus

Standard EVENTS

blur() Removes focus from an element

click() Executes a click on an element

cloneNode() Clones an element

focus() Gives focus to an element

Standard METHODS

className Sets or returns the class attribute of an element

clientHeight Returns the viewable height of the content on a page (not including borders, margins, or scrollbars)

clientWidth Returns the viewable width of the content on a page (not including borders, margins, or scrollbars)

disabled Sets or returns the disabled attribute of an element

height Sets or returns the height attribute of an element

id Sets or returns the id of an element

Standard PROPERTIES

attributes[] Returns an array of the attributes of an element

Standard COLLECTIONS

This is not the complete listing.

http://www.w3schools.com/jsref/met_html_blur.asp

http://www.w3schools.com/jsref/met_html_click.asp

http://www.w3schools.com/jsref/met_html_focus.asp

http://www.w3schools.com/jsref/prop_html_classname.asp

http://www.w3schools.com/jsref/prop_html_disabled.asp

http://www.w3schools.com/jsref/prop_html_id.asp

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CSS

159.339Cascading Style Sheets

• Method for specifying properties for HTML elements– default and specific fonts, colours etc.

• Allows easy modification of page styles– Style sheet can be modified rather than

editing the html• Style sheet can be embedded in HTML

or linked via an external file

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Selector Start ofblock

Declaration Declaration End of block

Example: h1 { color:blue; font-size:12px; }

Property:value; Property:value;

General syntax: Selector{ property:value; property:value;}

•The selector is normally the HTML element you want to style.•Each declaration consists of a property and a value.

CSS Structure and Syntax

159.339CSS Structure & Syntax

• CSS declarations always ends with a semicolon, and declaration groups are surrounded by curly brackets

• The comment syntax is just like in C-programming: /* this is a comment */

• You can specify and apply CSS-style formatting to an HTML element either by using an ID selector or a Class selector.

159.339Incorporating CSS

There are three ways of inserting a style sheet:•External style sheet•Internal style sheet•Inline style

159.3391. Incorporating CSS

External style sheet

<head> <link rel="stylesheet" type="text/css" href="mystyle.css" /></head>

• An external style sheet is ideal when the style is applied to many pages.

• With an external style sheet, you can change the look of an entire Web site by changing one file.

• The file should not contain any html tags.

• Each page must link to the style sheet using the <link> tag. The <link> tag goes inside the head section:


Example: External style sheet

<head> <link rel="stylesheet" type="text/css" href="mystyle.css“ ></head>

hr {color:sienna;}p {margin-left:20px;}body {background-image:url("images/back40.gif");}

mystyle.css

myHTML.htm


Internal style sheet

<head><style type="text/css"> hr {color:sienna;} p {margin-left:20px;} body {background-image:url("images/back40.gif");}</style></head>

• Suitable when a single document has a unique style.

• You define internal styles in the head section of an HTML page, by using the <style> tag, like this:


Inline style sheet (Inside an HTML element)

<p style="color:rgb(255,0,0);margin-left:20px"> Hello! </p>

• An inline style loses many of the advantages of style sheets by mixing content with presentation.

• To use inline styles you use the style attribute in the relevant tag. The style attribute can contain any CSS property.

• The example shows how to change the color and the left margin of a paragraph:

Avoid using the inline style!

159.339Cascading Order of Styles

Cascading multiple styles (the list is in increasing order of priority)

1. Browser default2. External style sheet3. Internal style sheet (in the head section)4. Inline style (inside an HTML element)

#4 has the highest priority.

Note: If the link to the external style sheet is placed after the internal style sheet in HTML <head>, the external style sheet will override the internal style sheet!

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• You can apply CSS-style formatting to an HTML element either by using an ID selector or a Class selector.

1. Applying CSS to an HTML element

ID SELECTOR•The id selector is used to specify a style for a single, unique element.•The id selector uses the id attribute of the HTML element, and is defined with a "#".•The style rule below will be applied to the element with id="para1":•Do NOT start an ID name with a number! It will not work in Mozilla/Firefox.

General Syntax: #ID-name{ Property:value; Property:value; /*... and so on.. */}

<h1 id=”ID-name”> Internet programming </h1>

ID selector application:

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2a. Applying CSS to an HTML element

class SELECTOR• The class selector is used to specify a style for a group of elements. Unlike the id

selector, the class selector is most often used on several elements.• This allows you to set a particular style for any HTML elements with the same class.• The class selector uses the HTML class attribute, and is defined with a "."General Syntax:

.class-name{ Property:value; Property:value; /*... and so on.. */}

<h1 class=”class-name”> Internet programming </h1><p class=”class-name”> Dynamic HTML: CSS, HTML, DOM, Javascript

</p>

class selector application:

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2b. Applying CSS to an HTML element

class SELECTOR

• You can also specify that only specific HTML elements should be affected by a class.

General Syntax:/* this class selector is only applicable to paragraphs*/

p.class-name{ Property:value; Property:value; /*... and so on.. */}

<p class=”class-name”> Dynamic HTML: CSS, HTML, DOM, Javascript </p>

class selector application:

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A continuously updated list of CSS properties can be found here: http://meiert.com/en/indices/css-properties/

CSS Text: http://www.w3schools.com/css/css_text.asp

CSS Demo: http://www.w3schools.com/css/demo_default.htm

CSS Tables: http://www.w3schools.com/css/css_table.asp

CSS Properties Index

http://meiert.com/en/indices/css-properties/

http://www.w3schools.com/css/css_text.asp

http://www.w3schools.com/css/demo_default.htm

http://www.w3schools.com/css/css_table.asp

159.339CSS Examples

• body {– font-family: Georgia, "Times New Roman", Times, serif; – color: blue; – background-color: #FFFF00 }

• Similarly any property can be specified and modified

• You can define your own selectors– .myStyle {color: blue}– Use with a class=“myStyle” attribute in the element you want to

modify

You will find more examples in our

website

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http://www.granneman.com/webdev/coding/css/centertables/

<div class="container"> <table class="table1"> ... </table> </div>

div.container { width:98%; margin:1%;}table.table1 { text-align:center; margin-left:auto; margin-right:auto; width:100px;}tr, td { text-align:left;}

Applying your CSS styles in a table

Center a Table with CSSCSS definitions: Centered, Fixed-width table

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Javascript

159.339JavaScipt

• A client-side scripting language– Allows building dynamic user interfaces

• Dynamic HTML elements• Client side animation

– Modify client view based on user input– Ability to check user input before forwarding to the

server• NOTE: JavaScipt and Java are different

– JavaScript is based on a standard ECMA scripting language, JavaScipt name adopted for marketing reasons (Java was starting to get hot at the time)

159.339JavaScript Basic Concepts

• JavaScript is an interpreted language– No need to compile the code

• The language is dynamically-typed– No need to declare the type of a variable– The type of a variable can change over time

• Need to be careful that the type is not changed accidentally by a programming mistake

• Structured Programming constructs– Similar to C– Case-sensitive like C

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• JavaScripts can be put in the <body> and in the <head> sections of an HTML page.

• To insert a JavaScript into an HTML page, we use the <script> tag.

• Inside the <script> tag we use the type attribute to define the scripting language.

Incorporating JavaScipt

<html><body> <script type="text/javascript"> /*...and so on.. */ </script></body></html>

159.339Incorporating JavaScipt

<html><body><script type="text/javascript"> </script><noscript> <h2>Your Browser doesn’t support JavaScript! </h2></noscript></body></html>

Handling browsers that do not support Javascript

– use HTML comments so that browsers that do not support JavaScript do not display your code

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Javascript in the <head> section

• By default, javascripts in a page is executed automatically when a page loads into the browser.

•However, we want to have control over when our scripts will be executed.

•Usually, we want them to be called when an event is triggered. In order to do this, we can write our scripts inside a function.

Incorporating JavaScipt into an HTML

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Javascript in the <head> section


<html><head><script type="text/javascript"> function message(){ alert("This alert box was invoked by an onload event."); }</script></head>

<body onload="message()"></body></html>

Put your functions in the <head> section. In this way, they are all written in one place, and they do not interfere with page content.

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Javascript in the <body> section


<html><head></head>

<body><script type="text/javascript"> document.write("My first JavaScript");</script></body>

</html>

• If you don't want your script to be placed inside a function, or if your script should write page content, it should be placed in the body section.

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Javascript in the <head> and <body> sections


• You can place an unlimited number of scripts in your document, so you can have scripts in both the <body> and the <head> sections.

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<html><head><script type="text/javascript" src=“filename.js"></script></head><body></body></html>

External Javascript file• If you want to run the same JavaScript on several pages, without having to write the same script on every page, you can write a JavaScript in an external file.

• Save the external JavaScript file with a .js file extension.

• Note: The external script cannot contain the <script></script> tags!

• To use the external script, point to the .js file in the "src" attribute of the <script> tag:

159.339JavaScript Programming Constructs

• All standard C operators can be used in JavaScript– +, -, *, /, +=, -=, ==, !=, <, >, >=, <=, %, &&,

||, !– Also can add strings (concatenate)

• Str3= Str1+ Str2;

– if, if … else, switch… case…, for …, while …, do … while

• Can all be used as in C

• The semicolon is optional (according to the JavaScript standard). It allows you to write multiple statements in one line.

159.339Variables

•JavaScript variables are used to hold values or expressions.

•A variable can have a short name, like x, or a more descriptive name, like carName.

•Rules for JavaScript variable names:• Variable names are case sensitive (y and Y are two

different variables)

• Variable names must begin with a letter or the underscore character

• Note: Because JavaScript is case-sensitive, variable names are case-sensitive.

159.339Variables

If you declare a variable within a function, the variable can only be accessed within that function. When you exit the function, the variable is destroyed. These variables are called local variables. You can have local variables with the same name in different functions, because each is recognized only by the function in which it is declared.

If you declare a variable outside a function, all the functions on your page can access it. The lifetime of these variables starts when they are declared, and ends when the page is closed.

159.339Variables

•A variable's value can change during the execution of a script. You can refer to a variable by its name to display or change its value.

•You can declare JavaScript variables with the var statement:ovar x;ovar userName=”Napoleon”; //use double quotes to assign a text value

•If you assign values to variables that have not yet been declared, the variables will automatically be declared.

•If you redeclare a JavaScript variable, it will not lose its original value.ovar z=100;ovar z;

A.If you add a number and a string, the result will be a string!

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Operator Description Example

== is equal to x==8 is false

=== is exactly equal to (value and type) x===5 is truex==="5" is false

!= is not equal x!=8 is true

> is greater than x>8 is false

< is less than x<8 is true

>= is greater than or equal to x>=8 is false

<= is less than or equal to x<=8 is true

Comparison Operators

greeting=(visitor=="PRES")?"Dear President ":"Dear ";

159.339JavaScript Functions

• Functions declared as in C– But no data types– E.g. myfun()

{ document.write(“myfunction”);}• Functions can take parameters

– E.g. myfun(X){ document.write(“Value:”+X);}

• Functions can return values– E.g. myfun(X,Y){ return X+Y;}

159.339Popup Boxes

Alert BoxAn alert box is often used if you want to make sure information comes through to the user.When an alert box pops up, the user will have to click "OK" to proceed. Confirm BoxA confirm box is often used if you want the user to verify or accept something.When a confirm box pops up, the user will have to click either "OK" or "Cancel" to proceed.

If the user clicks "OK", the box returns true. If the user clicks "Cancel", the box returns false. Prompt BoxA prompt box is often used if you want the user to input a value before entering a page.When a prompt box pops up, the user will have to click either "OK" or "Cancel" to proceed after entering an input value.

If the user clicks "OK" the box returns the input value. If the user clicks "Cancel" the box returns null.

159.339JavaScript Arrays• Zero-indexed arrays

– myArray = new Array(4);• Create and array of 4 elements

– myList = new Array(“one”, “two”, “three”);– first = myArray[0];

• myArray.length– Returns length of array (number of elements)

• pop() : Removes last element of array• push(“item1”, “item2”) : Adds items to the end of the array• shift(): Removes an item from the front of the array• unshift(“item1”): Adds items to the beginning of the array• concat(): Joins two or more arrays, returning a new array• join(delimiter): Joins the elements of an array into a string

using the delimiter

159.339Catching Errors

try{ //Run some code here}catch(err){ //Handle errors here}

• The try...catch statement allows you to test a block of code for errors.

• We would want to test our codes properly before making it publicly accessible.

• We can test our codes for any error by using the try and catch clauses.

159.339Catching ErrorsThrow statement • The exception can be a string, integer, Boolean or an object.

• Note that throw is written in lowercase letters. Using uppercase letters will generate a JavaScript error!

• The throw statement allows you to create an exception. If you use this statement together with the try...catch statement, you can control program flow and generate accurate error messages.

throw(exception)

Syntax:

159.339Catching Errors

<html><body><script type="text/javascript">var x=prompt("Enter a number between 0 and 10:","");try { if(x>10){ throw "Err1"; } else if(x<0){ throw "Err2"; } else if(isNaN(x)) { throw "Err3"; } }

catch(er) { if(er=="Err1“) { alert("Error! The value is too high"); } if(er=="Err2“) { alert("Error! The value is too low"); } if(er=="Err3“) { alert("Error! The value is not a number"); } }</script></body></html>

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• The HTML document is available to your javaScript code as an object tree.– The root of this tree is the document object.– All the elements in the document are built under this tree

• You can refer to each element using its element ID or Name– specify a unique name or id for each element

• We shall return to the Document Object Model later on when we look at XML.

HTML Document Object Model

159.339Examples

<select name="drink"><option value="2.50"> Coffee <option value="2.25"> Hot Cocoa<option value="1.00"> Chai </select>

HTML DROP-DOWN LIST

drop-down list: name:drink property:selectedindex property:value

159.339Examples

<input type=submit value="Order">

HTML Submit button

159.339Examples

<input type="radio" name="sizef" value="1">Tall<input type="radio" name="sizef" value="1.5">Grand<input type="radio" name="sizef" value="2"> Super

HTML RADIO BUTTONS

radio-buttons: name:sizef property:value property:checked property:length

159.339Examples

<input type="text" name="label" value=""><input type=text name="totalf" value="">

HTML TEXT FIELDS

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<body> <h2> Coffee shop </h2> <p>

<form name="orderf" onsubmit="return addup(this);" action=""><select name="drink"><option value="2.50">Coffee <option value="2.25">Hot Cocoa<option value="1.00">Chai </select> <br><input type="radio" name="sizef" value="1">Tall<input type="radio" name="sizef" value="1.5">Grand<input type="radio" name="sizef" value="2"> Super<input type=submit value="Order"> <br>

<br><input type="text" name="label" value=""><input type=text name="totalf" value="">

</form> </body>

Examples

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<script type="text/javascript">

function addup(f) {var total; var taxrate = .08 ; var drinkbase; var opts;

opts=f.drink;drinkbase = f.drink[opts.selectedIndex].value;var sizefactor; var i; var totals; var dp;

for (i=0;i<f.sizef.length;i++) { if (f.sizef[i].checked) { sizefactor = f.sizef[i].value; } }total = sizefactor * drinkbase;total = total*(1 + taxrate);f.label.value="Total with tax";f.totalf.value=total;totals = f.totalf.value + "00";

dp = totals.indexOf(".");if (dp<0) { f.totalf.value = "$" + f.totalf.value + ".00"; return false;}else {

totals = "$" + totals.substr(0,dp+3); //control the number of decimal places f.totalf.value = totals; return false;}

}</script>

javascript

Form: name:orderfdrop-down list: name:drink property:selectedindex property:value radio-buttons: name:sizef property:value property:checked property:lengthtext fields: name:label name:totalf property:value

HTML elements

string.indexOf(searchstring, start)

• The indexOf() method returns the position of the first occurrence of a specified value in a string.

• This method returns -1 if the value to search for never occurs.

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A submit button is used to send form data to a server. The data is sent to the page specified in the form's action attribute. The file defined in the action attribute usually does something with the received input:

<form name="input" action="html_form_action.asp" method="get"> Username: <input type="text" name="user" /> <input type="submit" value="Submit" /></form>

Sending data to a server

159.339Client-side (Browser) Objects

Window object: Represents an open window in a browser. Information about the windows this document is nested

in. not a W3C standard, but all major browsers support it.

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Navigator object: Information about the clients browser You can access this object to learn about the name,

version and platform where the browser was compiled. It also tells us if the browser is Java-enabled. not a W3C standard, but all major browsers support it.

History object: Information about the URLs visited by the user within the

browser’s window window.history

For more information on the history object: https://developer.mozilla.org/en/window.history

Screen object: Information about the clients screen (e.g. resolution, width

and height of the screen – excluding the taskbar not a W3C standard, but all major browsers support it. window.screen

Client-side (Browser) Objects

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Location object: window.location not a W3C standard, but all major browsers support it. Information about the current URL

o Hostname, port number, protocol, query portion

Client-side (Browser) Objects

159.339HTML DOM Collections

• anchors[]– An anchor object represents an HTML hyperlink (bookmark, URL).– Any anchors with a name or id

• applets[] • embeds[]

– List of embedded objects, browser must have appropriate viewer

• forms[] • images[] • links[]

– Any anchors with an href

159.339HTML DOM Properties

• body • cookie• domain

– Servers domain• referrer

– URL of document that loaded current document• title• URL

159.339HTML DOM Methods

• getElementById("id")– Not W3C standard

• getElementsByName("name")• open("mimetype"[,replace])• write("str") • writeln("str")• close()

159.339JavaScript Event Handling

• As the Page loads and the user interacts with the web page events are generated– onload: of document body– onmouseover, onmouseout, onclick,

ondblclick, onmousedown, onmouseup, onmousemove

– onfocus, onresize– onkeydown, onkeypress, onkeyup– onsubmit, onchange

159.339JavaScript Event Handling

• Let’s look at an event handling example

Javascript-16 - Events.html

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At the USENIX annual conference last month (June 2010), Gmail engineer Adam de Boor surprised the audience by noting that the company's Gmail service was written entirely in JavaScript, and that all of its code, around 443,000 lines worth, was written by hand.

How powerful is JavaScript?

http://infoworld.com/d/developer-world/google-executive-frustrated-java-c-complexity-375

This recent news says it all! ;)

This was taken from a news clip

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He noted that while Java is more expressive, it is also more verbose. "At this point to me it's a matter of choice which language you use," de Boor said.

JavaScript is one of a whole batch of languages -- others include Ruby and Python -- that have been developed over the past 10 years in response to the growing complexity of C++ and Java.

While having a simpler syntax, such languages have their drawbacks as well, he argued.



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These new languages tend to be slower, don't scale as well, and can harbor more errors, Pike elaborated.

The languages tend to be interpreted rather than compiled, meaning the programs written in such languages aren't compiled before running, so tend to run slower as a result. They also tend to be dynamically typed, meaning programmers don't need to specify what type of data their variables will hold.

"Dynamic typing is not necessarily good. You get static errors at run time which you really should be able to catch at compile time," he said.

With all this in mind, Pike then described Go as an attempt to fuse the best attributes of both sets of languages.



159.339Summary

Main points to remember:

• Dynamic web sites as opposed to static websites

• Cascading style sheets

• Javascript as a client-side programming language

• HTML Document Object Model

Exercises:

• Again, look at real web sites - this time those based on CSS and serve Javascript. Ask yourselves: What’s happening at the client side? What’s happening at the server side?

Documents

159.339 1 DHTML Dynamic Hypertext Markup Language Client-side Programming Lecture