Lecture 3 Javascript1

SFDV2001 – Web Development

Lecture 3: JavaScript

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History – Mechanical Programs Charles Babbage

Developed the first mechanical computation.

Created the Difference Engine. Designed the Analytical Engine.

Ada Byron, Lady Lovelace Described the uses of the Analytical

Engine. Helped create the first computer

program.

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History - Computability Alan Turing

Defined the set of all things that could be computed. Studied computability. Tests for Artificial Intelligence.

War hero Worked at Bletchley Park. Headed the group working on breaking the Enigma. Developed electronic machines to break codes.

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History – Modern Computers John von Neumann

Mathematician and Physicist. Worked on the H-bomb. Contributed to many areas.

Computer Design Processing unit. Memory. Input and output.

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Computer Design Central processing unit (CPU)

A central core that processes instructions . Increments a program counter. Has small internal storage.

Memory (RAM) An area to hold programs and data. Accessible from the CPU. An address for every location. Bus connects CPU to memory.

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Computer Design Input

Punch cards and switches. Keyboards, mouse, camera,... Scanners. GSR Galvanic Skin Response. nMRI.

Output Flashing lights, cards. Screens, printers, speakers,... Computer Aided Machining.

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Programming Writing programs for computing devices Remember

Sequence Selection Repetition

Central Processing Unit runs these instructions. Memory holds data. Input allows interaction. Output lets us see what is going on.

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Scripting A script is a list of stuff to do. Works through a application that interprets the

“script”. Scripting ability added to Netscape v2.0

Initially mocha then LiveScript. Simple instructions. New commands added over time.

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JavaScript JavaScript is NOT JAVA Similarity

both used on the web. similar syntax, based on C. Objects are important.

Not a universal standard Ecma standard script is similar.

IE implements similar script called JScript. Different bowsers different behaviour.

C

Java JavaScript

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JavaScript Provides tools for:

Mouse over events Checking Navigation Changing display

Uses include: Allows developer to do more than HTML Making pages responsive to the user Much of the early uses superseded by CSS

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Including JavaScript Script tag <script type=”....”> </script> HTML comment <!-- so old browsers do not try

to interpret it JavaScript comment // before the --> so

JavaScript does not try to interpret that bit

<script type=”text/javascript”><!--

javascript code//-->

</script>

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Commenting

HTML comments <!-- --> JavaScript comments /* */

to end of line //

Allows the developer to make notes and clarify issues.

Common comments include Author Dates and versions Problems and bugs Explanation of complex processes

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Variables A name for an object

var age = 31 Can be

numbers 31 text “simon” boolean true/false null

Example x = 5, y = 3 document.writeln(x + y); outputs 8

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Functions and Methods A block of instructions that are collected

together. Allows reuse of code. Makes things easier to read. Examples

document.write(“Hello World”); Date(); Math.sqrt(25);

A method is a function attached to an object.

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Parameters Variables or values passed to functions. document.writeln(“string”)

passed the string to write. window.open(“url”, “name”, “features”)

passed stings for: url, name features of the window

Math.sqrt(number) passed the number to square root.

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Examples MouseOver effects

Usually changing an image

Can do other things, like popups

CSS is better for mouse overs that just change images.

<img align=rightsrc="cosc_logo.jpg" onMouseOver = this.src="unilogo.gif"onMouseOut = this.src="cslogo.jpg">

<img align=rightsrc="cosc_logo.jpg" onMouseOver = this.src="unilogo.gif"onMouseOut = this.src="cslogo.jpg">

<img align=rightsrc="cosc_logo.jpg" onMouseOver = window.open(“http://www.otago.ac.nz”)>

Change to local examples

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Examples Popups

Those irritating new windows Blocked by lots of browsers and browser extensions

Last string for features such as toolbar, location, directories, status, menubar,.... width=pixels height=pixels

Please don't use popups

window.open(“http://www.otago.ac.nz”,”otago”,””)

window.open(“”,”otago”,”width=40,height=40”)

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Examples Form validation

Good use of JavaScript. Checks:

numbers are numbers dates are valid all data has been entered

Gives feedback about selected items

More about this next week

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Event Driven Programming Responding to things like

Mouse Clicks Keystrokes Windows opening Program termination

JavaScript responds to events rather than polling. Polling – Are we there yet?, Are we there yet?, Are

we there yet? Are.......... Event – Car stopping - “Are we there?”

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Next The DOM and JavaScript. More examples of JavaScript. Objects. Form validation.

Problems with JavaScript.