NAMEd anchors Enabling users to jump to specific points within Web documents

Anchors and HREFs We have seen that, to jump from one web document to another, we specify the URL of the target document in the href attribute of the tag which is linking to the target document However, we can also use a name as the value of a href attribute This is used to jump to a point in a document

Dictionary of Computin Acronyms List of Definitions Definition of a CPU Definition of RAM Definition of ROM CPU A CPU is a central processing unit. Blah blah blah blah blah blah blah blah blah blah blah blah blah Go back to List of Definitions.

We use tags in two places: –to specify the hot-links –to specify the targets of the hot-links An tag used to specify a hot-link target uses a name attribute instead of a href Example: List of Defns … …. Go to list of defns

An element can also point to a specific point in a different document Example –In document 1: A place in the middle of Document 2 –In document 2 A place in the middle of this document

Image maps Another way to form hot-links

On the next slide, the image showing the Middle East can be used to link to other web documents

Clicking the dotted area below hot-links to a docm’nt on Turkey

Clicking the dotted area below hot-links to a docm’t on the Med

Clicking the dotted area below hot-links to a docm’nt on Egypt

#image1 {width:140; neight:200} ….

To use an img to provide hot-links, we need two things: –the img, which must have an explicitly stated width and height –a map of this img, which specifies what areas within the image are hot-links The map must have a name attribute The img must refer to the map which has this name

#image1 {width:140; neight:200} …. …

The map is delimited by and tags Between these tags, we must have a series of tags Each tag must have two attributes –a coords attribute which specifies the upper-left and lower-right corners of the area –a href attribute which specifies the document to which the area forms a hot-link

….

Map areas do not have to be rectangular

Cs 3314 got here on 8/11/2007

Dynamic Web Pages

Static Web Pages The web pages that we have created so far do not change after they are loaded by a browser -- they are static They provide only one feature that supports interactivity -- hotlinks Most hotlinks impose a lot of traffic on the Internet and impose a lot of computing load on servers

Dynamic Web Pages Static web pages are good but good is never enough in the world of Information Technology As soon as static web pages were available, the desire arose for pages which were more interactive and which reduced the load on the Internet and on web servers People wanted more intelligence in web pages

Adding intelligence to web pages To add intelligence to any computer entity, we must write a program which implements that intelligence There are two places where the programs can be executed: –on a server –on a broswer

Server-side versus Client-side Choosing between server-side and client- side programming depends on several factors: –Privacy how private do you want your program to be will the program manipulate private data? –Loading are you concerned about overloading your server are you concerned about the Internet

Server-side programming Advantages –Programs can be kept private: users only see the output that your program send to them –Data can be kept private –Data can be kept permanently Disadvantages –adds to server workload –adds to network traffic –delays response to user

Client-side programming Advantages –client computer does all the work –reduces traffic between server and client –enables faster response to user Disadvantages –users can see your program –users can see your data –programs cannot really keep permanent data because users can throw them away

Types of client-side programs Applets: –can avail of full power of general programming languages (Java is the one usually used); –can be compiled and, therefore, semi-private Scripts –written in simpler languages (Javascript, VBscript) developed specifically for the task –interpreted not compiled

Client-side programming with Javascript

Don’t be caught by the name Javascript is NOT Java History of Javascript: –Netscape were already developing a scripting language (called LiveScript, I think) when Sun proposed Java as a platform-independent general programming language –there was a bit of mutual band-wagon jumping some syntax blending change of name from LiveScript(?) to Javascript

What can Javascript programs do? Handle browser and/or user events create new browser frames and windows process forms process “cookies” interface with applet and server-side programs control multi-media objects on a web page

User-event Handling

Types of user events when the mouse button is clicked on an element; when the mouse button is double-clicked on an element; when the mouse button is pressed over an element; when the mouse button is released over an element; when the mouse is moved onto an element;

Types of user events (contd.) when the mouse is moved while over an element; when the mouse is moved away from an element; when a key is pressed and released over an element; when a key is pressed down over an element; when a key is released over an element.

Consider following web page It has two paragraphs of text While user moves mouse onto first paragraph, its font size will increase While user moves mouse away from second paragraph, its color will change to red

How did he do that? By associating two very short Javascript programs with each paragraph, each program with a different event: –First paragraph: one program executes when mouse enters box other program executes when mouse leaves box –Second paragraph: one program executes when mouse enters box other program executes when mouse leaves box

Associating programs with events Events happen to content elements So, contents elements can have attributes whose –names indicate the events we want to handle and –whose values are the Javascript programs we want to execute when these events occur

Names for events onclick, when the mouse button is clicked on an element; ondblclick, when the mouse button is double-clicked on an element; onmousedown, when the mouse button is pressed over an element; onmouseup, when the mouse button is released over an element; onmouseover, when the mouse is moved onto an element; onmousemove, when the mouse is moved while over an element; onmouseout, when the mouse is moved away from an element; onkeypress, when a key is pressed and released over an element; onkeydown, when a key is pressed down over an element; onkeyup, when a key is released over an element.

Extract from HTML specification <p onmouseover='this.style.fontSize=32' onmouseout='this.style.fontSize=14'> Whenever you place your mouse over me, my Font Size will increase to help you read me.

Analysis of extract: <p onmouseover='this.style.fontSize=32' onmouseout='this.style.fontSize=14'> Attributes are of form: someEventName=‘someJavascript’

Analysis continued onmouseover='this.style.fontSize=32' Javascript is enclosed by apostrophes Case is ESSENTIAL in Javascript this (note all lower-case) refers to the element to which the Javascript is attached this.style refers to the style for this element this.style.fontSize refers to the font-size property of the style for this element

Another extract from HTML spec <p onmouseover='this.style.color="red"' onmouseout='this.style.color="black"'> this.style.color refers to the color property of the style for this paragraph the values specified for the color must be enclosed in quotes

Full HTML specification Simple Mouse Event Some Subject or Other Whenever you place your mouse over me, my Font Size will increase to help you read me. Another Subject Whenever you place your mouse over me, my color will change to help you read me.