Client-side Programming Dynamic Hypertext Markup Language

Name: Client-side Programming Dynamic Hypertext Markup Language
Uploaded: 2017-10-01T18:29:41+00:00
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Channel: Polly Carpenter
Description: Client-side Programming Dynamic Hypertext Markup Language

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

What is DHTML? CSS Javascript Topics for Discussion DOM, Examples

Cascading style sheets, HTML, DOM and Javascript
Dynamic HTML Cascading style sheets, HTML, DOM and Javascript

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

HTML Element

This is not the complete listing.
HTML ELEMENT Standard PROPERTIES 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 METHODS blur() Removes focus from an element click() Executes a click on an element cloneNode() Clones an element focus() Gives focus to an element Standard EVENTS This is not the complete listing. 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 COLLECTIONS attributes[] Returns an array of the attributes of an element

Cascading 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

CSS Structure and Syntax
General syntax: Selector{ property:value; property:value;} Selector Start of block Declaration End of block Example: h1 { color:blue; font-size:12px; } Property:value; The selector is normally the HTML element you want to style. Each declaration consists of a property and a value.

CSS 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.

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

1. Incorporating CSS External style sheet
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: <head> <link rel="stylesheet" type="text/css" href="mystyle.css" /> </head>

1. Incorporating CSS Example: External style sheet hr {color:sienna;}
mystyle.css hr {color:sienna;} p {margin-left:20px;} body {background-image:url("images/back40.gif");} myHTML.htm <head> <link rel="stylesheet" type="text/css" href="mystyle.css“ > </head>

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

Avoid using the inline style!
3. Incorporating CSS Inline style sheet (Inside an HTML element) 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: <p style="color:rgb(255,0,0);margin-left:20px"> Hello! </p> Avoid using the inline style!

Cascading Order of Styles
Cascading multiple styles (the list is in increasing order of priority) 1. Browser default 2. External style sheet 3. Internal style sheet (in the head section) 4. Inline style (inside an HTML element) 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! #4 has the highest priority.

1. Applying CSS to an HTML element
You can apply CSS-style formatting to an HTML element either by using an ID selector or a Class selector. 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; /*... and so on.. */ } ID selector application: <h1 id=”ID-name”> Internet programming </h1>

2a. Applying CSS to an HTML element
You can apply CSS-style formatting to an HTML element either by using an ID selector or a Class selector. 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; /*... and so on.. */ } class selector application: <h1 class=”class-name”> Internet programming </h1> <p class=”class-name”> Dynamic HTML: CSS, HTML, DOM, Javascript </p>

2b. Applying CSS to an HTML element
You can apply CSS-style formatting to an HTML element either by using an ID selector or a Class selector. 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; /*... and so on.. */ } class selector application: <p class=”class-name”> Dynamic HTML: CSS, HTML, DOM, Javascript </p>

CSS Properties Index A continuously updated list of CSS properties can be found here: CSS Text: CSS Demo: CSS Tables:

You will find more examples in our website
CSS 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

Center a Table with CSS CSS definitions: Centered, Fixed-width table 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 <div class="container"> <table class="table1"> ... </table> </div>

Javascript

JavaScipt 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)

JavaScript 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

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

Incorporating JavaScipt
Handling browsers that do not support Javascript <html> <body> <script type="text/javascript">  </script> <noscript> <h2>Your Browser doesn’t support JavaScript! </h2> </noscript> </body> </html> use HTML comments so that browsers that do not support JavaScript do not display your code

Incorporating JavaScipt into an HTML
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.

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.

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.

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.

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

JavaScript 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.

Variables 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.

Variables  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.

Variables 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: var x; var 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. var z=100; var z; If you add a number and a string, the result will be a string!

Comparison Operators Operator Description Example == is equal to x==8 is false === is exactly equal to (value and type) x===5 is true x==="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 greeting=(visitor=="PRES")?"Dear President ":"Dear ";

JavaScript 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;}

Popup Boxes Alert Box An 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 Box A 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 Box A 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.

JavaScript 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

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

Catching Errors Throw 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. Syntax: throw(exception)

Catching Errors <html> catch(er) <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>

HTML Document Object Model
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.

Examples HTML DROP-DOWN LIST <select name="drink">
<option value="2.50"> Coffee <option value="2.25"> Hot Cocoa <option value="1.00"> Chai </select> drop-down list: name:drink property:selectedindex property:value

Examples HTML Submit button <input type=submit value="Order">

Examples HTML RADIO BUTTONS
<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 radio-buttons: name:sizef property:value property:checked property:length

Examples HTML TEXT FIELDS
<input type="text" name="label" value=""> <input type=text name="totalf" value="">

Examples <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>

javascript HTML elements Form: name:orderf drop-down list: name:drink
<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; </script> HTML elements Form: name:orderf drop-down list: name:drink property:selectedindex property:value radio-buttons: name:sizef property:checked property:length text fields: name:label name:totalf 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.

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

Client-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.

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: Screen object: Information about the clients screen (e.g. resolution, width and height of the screen – excluding the taskbar window.screen

Location object: window.location not a W3C standard, but all major browsers support it. Information about the current URL Hostname, port number, protocol, query portion

HTML DOM Collections anchors[] applets[] embeds[] forms[] images[]
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

HTML DOM Properties body cookie domain Servers domain referrer
URL of document that loaded current document title URL

HTML DOM Methods getElementById("id") getElementsByName("name")
Not W3C standard getElementsByName("name") open("mimetype"[,replace]) write("str") writeln("str") close()

JavaScript 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

JavaScript Event Handling
Let’s look at an event handling example Javascript-16 - Events.html

This recent news says it all! ;)
How powerful is JavaScript? This was taken from a news clip 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. This recent news says it all! ;)

This was taken from a news clip
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.

This was taken from a news clip
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.

Summary 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?

Client-side Programming Dynamic Hypertext Markup Language

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