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77103 Programming for Interactive Media

77103 Programming for Interactive Media. Lectorial 2.02abc – First Contact after this session, you should be able to avoid the cut-and-paste mentality  add simple Javascript to a website confidently explore what Javascript can offer you

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77103 Programming for Interactive Media

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  1. 77103 Programming for Interactive Media Lectorial 2.02abc – First Contact after this session, you should be able to avoid the cut-and-paste mentality  add simple Javascript to a website confidently explore what Javascript can offer you references - please do some further reading later book : "DOM Scripting" : Jeremy Keith (2005) online tutorials and documentation at http://domscripting.com http://www.w3schools.com/js http://www.w3schools.com/jsref Paul Warren - pim 2.02abc

  2. What is Javascript ? • Javascript (aka JS, or ActiveScript, or ECMAScript) is a powerful modern programming language • designed to enhance the capabilities of a web page • the script writer (you) can specify how the page reacts to various events • mouse actions • timers • faults and errors • inputs and other data • your reaction usually takes the form of changing part of the HTML on the current web page • today we will cover just a few basic examples • read up further as you become confident • not related to the Java programming language Paul Warren - pim 2.02abc

  3. How does JS run ? user browses toweb document HTML docloads up stylesheets& rendering wait for event JS main programis executed onclickonmouseoverondblclickonkeypress executerelevantfunction Paul Warren - pim 2.02abc

  4. 1st example : "Hello World" • we often introduce programming by showing you the simplest possible program • the program uses JavaScript to print "Hello World!" on a webpage that would otherwise otherwise be totally blank • we need : • a blank html file helloworld.htm • a javascript file helloworld.js • a <script> tag linking to the javascript file • see separate handouts • the javascript program adds some extra text to the document by modifying the Document Object Model (DOM) of the webpage document.body.innerHTML = "Hello, World!"; • this changes the contents of the <body> tag of the document • it's called an assignmentstatement (basically, a copy command) • the browser window contents change accordingly Paul Warren - pim 2.02abc

  5. about variables • a variable is an area of the computer's RAM that is used to hold a piece of data, and which can be varied (changed) (obviously !) • variables can hold things like names, numbers, dates, etc. • think of it like a box with something in it (possibly empty) • example: price = 3.75; vat = price * 0.15; total = price + vat; • if you change a variable, its previous contents are discarded • all the parts of your web document are also held in variables • examples: document document.body document.body.innerHTML • if you give an id to a tag, it can be used as a variable • tag: <img id="pic1" src="coffee.jpg" /> • variable name: document.getElementById("pic1") Paul Warren - pim 2.02abc

  6. the Document Object Model html body head ul title h1 img meta p li li li Paul Warren - pim 2.02abc

  7. using JS to change the DOM • once we have a tag with an id, we can change any part of the tag • original HTML:<img id="pic1" src="coffee.jpg" /> • variable name:document.getElementById("pic1").src = "tea.jpg"; • HTML changes to:<img id="pic1" src="tea.jpg" /> • Your turn: • write a paragraph tag with an id and some text • write a JS statement to replace the text with an img tag Paul Warren - pim 2.02abc

  8. 2nd example : form information • information entered into a form by the user can be accessed in JS • the HTML: <form onsubmit="greet();"> Please enter your name: <input type="text" id="box"></input> </form> • the javascript: function greet() { name = document.getElementById("box").value; document.body.innerHTML += "Hi, " + name + ", Welcome!"; } • the JS greet function is called when the onsubmit event triggers Paul Warren - pim 2.02abc

  9. Exercises • For all today's activities, please work with your "pair partner" • coding exercise: • write an HTML/JS combination that asks for the user's weight • input the weight in two boxes: stones and pounds • work out what you have to do to convert the weight into a total number of pounds, and from there into kilograms • display the user's weight in kilograms, with a cheery message • there are 14 pounds in 1 stone • there are 2.2 pounds in 1 kilogram • algorithm exercise: • develop an algorithm for turning to a page number in a book as efficiently as possible. The number of steps is more important than the time taken to find the page. Paul Warren - pim 2.02abc

  10. final notes • Javascript (JS) is a powerful programming language • JS is the "behaviour" part of the Web trinity • alongside HTML and CSS • Web standards are recommended • try to keep your JS in a separate file • always consider users who have no JS capabilities • JS is best written in an event-action form • many useful consequences • e.g. makes it easier to provide separate webpages for different languages, using the same JS program • your marks in this course will depend on you writing program code which is : • well-designed (as simple as possible) • working correctly • tidy and readable Paul Warren - pim 2.02abc

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