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Lecture 9

Lecture 9. 21/11/12. Comments in JavaScript. // This is a single line JavaScript comment <!-- -- >. For Loops. Executes a statement or statements for a number of times – iteration. Syntax for(initialize; test; increment) { // statements to be executed }

merritt-baldwin
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Lecture 9

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  1. Lecture 9 21/11/12

  2. Comments in JavaScript • // This is a single line JavaScript comment • <!-- -- >

  3. For Loops • Executes a statement or statements for a number of times – iteration. • Syntax for(initialize; test; increment) { // statements to be executed } • Initial Value is the starting number of the loop. • If the condition(test) is true the code is executed. • The initial value is changed by the step size.

  4. For Loops • The expression is evaluated, if it is false, JavaScript moves to the next statement in the program • If it is true then the statement is executed and expression is evaluated again • Again if the expression is false the JavaScript moves on the next statement in script, otherwise it executes the statement that forms the body of the loop

  5. For Loops <html> <head> <title> For</title> </head> <body> <script type="text/javascript"> for (i=0;i<= 5; i++) //the position of the ++ here does not have an impact on the output it will always start at 0 { document.write("The number is " + i);// change to i++ and ++i here to see the impact on the output document.write("<br />"); } </script> </body> </html>

  6. Another Example <html> <head> <title> For</title> </head> <body> <script type="text/javascript"> for (i=0;i<= 5; i++) //the position of the ++ here does not have an impact on the output it will always start at 00 { document.write("The number is " +i++); document.write("<br />"); } </script> </body> </html> The number is 0The number is 2The number is 4

  7. Another Example <html> <head> <title> For</title> </head> <body> <script type="text/javascript"> for (i=0;i<= 5; i++) //the position of the ++ here does not have an impact on the output it will always start at 00 { document.write("The number is " + ++i); document.write("<br />"); } </script> </body> </html> The number is 1The number is 3The number is 5

  8. For Loop Another Example • The counter variable is something that is created and usually used only in the for loop to count how many times the for loop has looped. • i is the normal label for this counter variable and what we will be using. • The conditional statement- • It is what decides whether the for loop continues executing or not. This check usually includes the counter variable in some way. • The counter variable is incremented after every loop in the increment section of the for loop. • The code that is executed for each loop through the for loop. <html> <script type="text/javascript"> <!-- varlinebreak = "<br />"; document.write("For loop code is beginning"); document.write(linebreak); for(i = 2; i < 10; i++) { document.write("Counter i = " + i); document.write(linebreak); } document.write("For loop code is finished!"); </script> </html>

  9. While Loops: • While a condition is true execute one or more statements. • “While Loops” are especially useful when you do not know how many times you have to loop • but you know you should stop when you meet the condition, i.e. an indeterminate loop

  10. While Loop • The while Loop is the basic statement that allows JavaScript to perform repetitive actions. It has the following syntax. while (expression) { // Statement to be executed } … more code…

  11. While Loops • This cycle continues until the expression evaluates to false • It is important that a Loop counter that is used within the body of the Loop is declared outside it.

  12. <html> <body> <script type="text/javascript"> i=0; while (i<=5) { document.write("The number is " + i); document.write("<br />"); i++; } </script> </body> </html>

  13. While Loops <html> <body> <script type="text/javascript"> i=1; while (i<=5) { document.write("The number is " + i); document.write("<br />"); i++; } </script> </body> </html> What happens in this example? <html> <body> <script type="text/javascript"> i=6; while (i<=5) { document.write("The number is " + i); document.write("<br />"); i++; } </script> </body> </html> Loop DOES not run

  14. While Another Example • There are two key parts to a JavaScript while loop: • The conditional statement which must be True for the while loop's code to be executed. • The while loop's code that is contained in curly braces "{ and }" will be executed if the condition is True. <html> <script type="text/javascript"> <!-- varmyCounter = 0; varlinebreak = "<br />"; document.write("While loop is beginning"); document.write(linebreak); while(myCounter < 10){ document.write("myCounter = " + myCounter); document.write(linebreak); myCounter++; } document.write("While loop is finished!"); </script> </html>

  15. Do While Loops <html> <body> <script type="text/javascript"> vari=0; do   { document.write("Output= " + i); document.write("<br />"); i++;   } while (i<=12); </script> </body> </html> Will run once to evaluate condition – <html> <body> <script type="text/javascript"> vari=13; do   { document.write("Output= " + i); document.write("<br />"); i++;   } while (i<=12); </script> </body> </html>

  16. Do While Another Example.. <script type="text/javascript"> <!-- var count = 0; document.write("Starting Loop" + "<br />"); Do { document.write("Current Count : " + count + "<br />"); count++; } while (count < 0); document.write("Loop stopped!"); //--> </script>

  17. Why use Loops? • When you want the same block of code to run over and over again in a row • Instead of adding several almost equal lines in a script we can use loops to perform a task like this While v For • A while loop doesn't initialize or increment any fields automatically as part of the command, it just tests a condition and executes the loop for as long as the condition remains true • A while loop can easily be substituted wherever you have a for loop by moving the initialization statement (e.g. i=1) in front of the loop and the increment statement (e.g. i++) to just inside the end of the loop • This may make the loop easier to read

  18. Length() <script type="text/javascript"> varmyString = "123456"; document.write("The string is this long: " + myString.length); myString = myString + "7890"; document.write("<br />The string is now this long: " + myString.length); </script>

  19. IndexOf Another Example… <html> <script type="text/javascript"> varaURL = "http://www.ucc.ie"; varaPosition = aURL.indexOf("ucc"); document.write("The position of ucc = " + aPosition); </script> </html>

  20. Substring and substranother example.. <script type="text/javascript"> varstr="End of term is near!"; document.write(str.substring(4)+"<br />"); document.write(str.substring(4,7)); </script> <script type="text/javascript"> varstr="Hello world!"; document.write(str.substr(3)+"<br />"); document.write(str.substr(3,4)); </script>

  21. CharAt () <html> <head> <title>JavaScript String charAt() Method</title> </head> <body> <script type="text/javascript"> varstr = new String( "This is string" ); document.writeln("str.charAt(0) is:" + str.charAt(0)); document.writeln("<br />str.charAt(1) is:" + str.charAt(1)); document.writeln("<br />str.charAt(2) is:" + str.charAt(2)); document.writeln("<br />str.charAt(3) is:" + str.charAt(3)); document.writeln("<br />str.charAt(4) is:" + str.charAt(4)); document.writeln("<br />str.charAt(5) is:" + str.charAt(5)); </script> </body> </html>

  22. Operators… <script type="text/JavaScript"> <!-- var two = 2 var ten = 10 varlinebreak = "<br />" document.write("two plus ten = ") var result = two + ten document.write(result) document.write(linebreak) document.write("ten * ten = ") result = ten * ten document.write(result) document.write(linebreak) document.write("ten / two = ") result = ten / two document.write(result) //--> </script> </body>

  23. Another If Else <script type="text/javascript"> var username = "Agent006"; if(username == "Agent007") document.write("Welcome special agent 007"); else document.write("Access Denied!"); document.write("<br /><br />Would you like to try again?<br /><br />"); // User enters a different name username = "Agent007"; if(username == "Agent007") document.write("Welcome special agent 007"); else document.write("Access Denied!"); </script>

  24. Form Validation Example <html> <head> <script language="javascript"> var x; varfirstname; var country1; var email; var phone1; var comment1; var at; var dot; function validate1() { x=document.myForm; at=x.myEmail.value.indexOf("@"); dot=x.myEmail.value.indexOf("."); firstname=x.myname.value; country1=x.country.value; email=x.myEmail.value; phone1=x.phone.value; comment1=x.comment.value;

  25. if (firstname =="") { alert("You must complete the name field"); x.myname.focus(); return false; } else if(isNaN(firstname)== false) { alert("Please enter your name correctly"); x.myname.focus(); return false; } else if (country1 =="") { alert("You must complete the country field"); x.country.focus(); return false; } else if(isNaN(country1)== false) { alert("Please enter country correctly"); x.country.focus(); return false; } else if(email == "") { alert("Please enter a vaild e-mail address"); x.myEmail.focus(); return false; }

  26. else if (at==-1) { alert("Please enter a vaild e-mail address "); x.myEmail.focus(); return false; } else if (dot==-1) { alert("Please enter a vaild e-mail address "); x.myEmail.focus(); return false; } else if(phone1=="") { alert("Please enter your phone number"); x.phone.focus(); return false; } else if(isNaN(phone1)==true) { alert("That phone number is not valid"); x.phone.focus(); return false; } else if(comment1=="") { alert("Please enter your comment!"); x.comment.focus(); return false; } return true; } </script>

  27. </head> <body> <form name="myForm" action="submitform.html" onSubmit="return validate1();"> Enter your First Name: <input type="text" name="myname"> <br> Enter your Country: <input type="text" name="country"> <br> Enter your e-mail: <input type="text" name="myEmail"> <br> Enter your Phone Number: <input type="text" name="phone"> <br> Your Comment: <input type="textarea" name="comment"> <br> <input type="submit" value="Send input"> </form> </body> </html>

  28. CSS Recap • Inline • Internal • External • Browser Default • Ref to external CSS <head>< link rel="stylesheet" type="text/css" href="mystyle.css" />< /head>

  29. CSS Rules • Inline – <p style="color:red;margin-left:20px">This is a paragraph.</p> • Internal <head> <style type="text/css">hr {color:blue;}p {margin-left:20px;}body {background-image:url("images/back40.gif");}< /style> </head> • External Create page and save as style1.css (example) h3{text-align:right;font-size:20pt;}

  30. CSS • Relative Font Measurements • em, ex, px • Absolute • in, cm, mm, pt, pc • Positioning • Absolute – When you specify position:absolute, the element is removed from the document and placed exactly where you tell it to go. • Relative – If you specify position:relative, then you can use top or bottom, and left or right to move the element relative to where it would normally occur in the document. • Z-index - The z-index property specifies the stack order of an element. • An element with greater stack order is always in front of an element with a lower stack order. • Note: z-index only works on positioned elements (position:absolute, position:relative, or position:fixed). • <div> • The <div> tag defines a division or a section in an HTML document. • The <div> tag is often used to group block-elements to format them with styles. • Div id • Specifies a unique id for an element • Generally ids are used for the main elements of the page, such as header, main content, sidebar, footer, etc. id attribute

  31. MCQ – IS6116 • MONDAY 5THDEC 1PM • 10% • BRING PENCIL • 30 MINUTES • 30 QUESTIONS • NEGATIVE MARKING +3 -1 • NO ANSWER 0

  32. Course Content to 5/12/11 • Website Design and Usability • Introduction to xHTML • Basic xHTMLTags • AdditonalxHTMLtag • Cascading Style Sheets • Introduction to Client Side Processing

  33. Summary • JavaScript-Variables and Operators • Control Flow Structures • Forms and String Object

  34. Every JavaScript statement should end with a _______ • Colon • Semi-colon • Curly bracket • None of the above • Methods ____ and ____ of the _____ object write xHTML text into an xHTML document. • Document, window and string • write, writeln and document • Lastindexof, indexof and string • None of the above • Like JAVA variables JavaScript variables are typed. • True or False. • You may only place JavaScript in the <head> tag in the xHTML document. • True or False.

  35. Sample Question What is the outcome from the following JavaScript code? <html> <head> <script type="text/javascript"> function mymessage() { alert("Hello World") } </script> </head> <body onload="mymessage()"> </body> </html> • A syntax error occurs • “Hello World” is printed to the browser window • An alert box is triggered by the onload event • The function triggers the onload event

  36. Sample Question What is the output from the following JavaScript code? <html> <head> <title> Char At</title> <script language="javascript"> var a; a="MCQ’s are great!"; document.write(x.charAt(6)); </script> </head> <html> • s • ’ • a • It will generate an error.

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