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JavaScript for Client-Side Programming: Scripts, Languages, and Tasks, Slides of Web Programming and Technologies
An introduction to client-side programming using javascript. It covers the differences between scripts and programs, the various scripting languages including javascript, jscript, and vbscript, and common tasks for client-side scripts such as form validation, image rollovers, and handling cookies. The document also discusses the limitations of client-side scripting and the use of the date object.
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2011/2012
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Download JavaScript for Client-Side Programming: Scripts, Languages, and Tasks and more Slides Web Programming and Technologies in PDF only on Docsity! COMP519: Web Programming Autumn 2011 client-side programming with JavaScript scripts vs. programs JavaScript vs. JScript vs. VBScript common tasks for client-side scripts JavaScript data types & expressions control statements functions & libraries strings & arrays Date, document, navigator, user-defined classes docsity.com Client-Side Programming • HTML is good for developing static pages can specify text/image layout, presentation, links, … Web page looks the same each time it is accessed in order to develop interactive/reactive pages, must integrate programming in some form or another • client-side programming programs are written in a separate programming (or scripting) language e.g., JavaScript, JScript, VBScript programs are embedded in the HTML of a Web page, with (HTML) tags to identify the program component e.g., <script type="text/javascript"> … </script> the browser executes the program as it loads the page, integrating the dynamic output of the program with the static content of HTML could also allow the user (client) to input information and process it, might be used to validate input before it’s submitted to a remote server docsity.com JavaScript • JavaScript code can be embedded in a Web page using <script> tags the output of JavaScript code is displayed as if directly entered in HTML <html> <!–- COMP519 js01.html 16.08.06 --> <head> <title>JavaScript Page</title> </head> <body> document.write displays text in the page text to be displayed can include HTML tags the tags are interpreted by the browser when the text is displayed <script type="text/javascript"> // silly code to demonstrate output document.write("<p>Hello world!</p>"); document.write(" <p>How are <br/> " + " <i>you</i>?</p> "); </script> <p>Here is some static text as well.</p> </body> </html> as in C++/Java, statements end with ; but a line break might also be interpreted as the end of a statement (depends upon browser) JavaScript comments similar to C++/Java // starts a single line comment /*…*/ enclose multi-line comments view page docsity.com JavaScript Data Types & Variables • JavaScript has only three primitive data types String : "foo" 'how do you do?' "I said 'hi'." "" Number: 12 3.14159 1.5E6 Boolean : true false *Find info on Null, Undefined <html> <!–- COMP519 js02.html 16.08.06 --> <head> <title>Data Types and Variables</title> </head> assignments are as in C++/Java message = "howdy"; pi = 3.14159; variable names are sequences of letters, <body> <script type="text/javascript"> var x, y; x= 1024; y=x; x = "foobar"; document.write("<p>x = " + y + "</p>"); document.write("<p>x = " + x + "</p>"); </script> </body> </html> digits, and underscores that start with a letter or an underscore variables names are case-sensitive you don't have to declare variables, will be created the first time used, but it’s better if you use var statements var message, pi=3.14159; variables are loosely typed, can be assigned different types of values (Danger!) view page docsity.com JavaScript Operators & Control Statements <html> <!–- COMP519 js03.html 08.10.10 --> <head> <title>Folding Puzzle</title> </head> <body> <script type="text/javascript"> var distanceToSun = 93.3e6*5280*12; var thickness = .002; standard C++/Java operators & control statements are provided in JavaScript • +, -, *, /, %, ++, --, … • ==, !=, <, >, <=, >= • &&, ||, !,===,!== • if , if-else, switch • while, for, do-while, … var foldCount = 0; while (thickness < distanceToSun) { thickness *= 2; foldCount++; } document.write("Number of folds = " + foldCount); </script> </body> </html> PUZZLE: Suppose you took a piece of paper and folded it in half, then in half again, and so on. How many folds before the thickness of the paper reaches from the earth to the sun? *Lots of information is available online view page docsity.com User-Defined Functions • function definitions are similar to C++/Java, except: no return type for the function (since variables are loosely typed) no variable typing for parameters (since variables are loosely typed) by-value parameter passing only (parameter gets copy of argument) function isPrime(n) // Assumes: n > 0 // Returns: true if n is prime, else false { if (n < 2) { Can limit variable scope to the function. if the first use of a variable is preceded return false; } else if (n == 2) { return true; } else { for (var i = 2; i <= Math.sqrt(n); i++) { if (n % i == 0) { return false; } } return true; } } with var, then that variable is local to the function for modularity, should make all variables in a function local docsity.com Function Example <html> <!–- COMP519 js06.html 16.08.2006 --> <head> <title>Prime Tester</title> <script type="text/javascript"> function isPrime(n) // Assumes: n > 0 // Returns: true if n is prime { // CODE AS SHOWN ON PREVIOUS SLIDE } </script> Function definitions (usually) go in the <head> section <head> section is loaded first, so then the function is defined before code </head> <body> <script type="text/javascript"> testNum = parseFloat(prompt("Enter a positive integer", "7")); if (isPrime(testNum)) { document.write(testNum + " <b>is</b> a prime number."); } else { document.write(testNum + " <b>is not</b> a prime number."); } </script> </body> </html> in the <body> is executed (and, therefore, the function can be used later in the body of the HTML document) view page docsity.com Another Example <html> <!–- COMP519 js07.html 11.10.2011 --> <head> <title> Random Dice Rolls Revisited</title> <script type="text/javascript"> function randomInt(low, high) // Assumes: low <= high // Returns: random integer in range [low..high] { return Math.floor(Math.random()*(high-low+1)) + low; } </script> </head> <body> recall the dynamic dice page could define a function for generating random <div style="text-align: center"> <script type="text/javascript"> roll1 = randomInt(1, 6); roll2 = randomInt(1, 6); document.write("<img src='http://www.csc.liv.ac.uk/"+ "~martin/teaching/comp519/Images/die" + roll1 + ".gif'/>"); document.write(" "); document.write("<img src='http://www.csc.liv.ac.uk/"+ "~martin/teaching/comp519/Images/die" + roll2 + ".gif'/>"); </script> </div> </body> </html> numbers in a range, then use whenever needed easier to remember, promotes reuse view page docsity.com JavaScript Objects • an object defines a new type (formally, Abstract Data Type) encapsulates data (properties) and operations on that data (methods) • a String object encapsulates a sequence of characters, enclosed in quotes properties include length : stores the number of characters in the string methods include charAt(index) : returns the character stored at the given index (as in C++/Java, indices start at 0) substring(start, end) : returns the part of the string between the start (inclusive) and end (exclusive) indices toUpperCase() : returns copy of string with letters uppercase toLowerCase() : returns copy of string with letters lowercase to create a string, assign using new or (in this case) just make a direct assignment (new is implicit) word = new String("foo"); word = "foo"; properties/methods are called exactly as in C++/Java word.length word.charAt(0) docsity.com String example: Palindromes function strip(str) // Assumes: str is a string // Returns: str with all but letters removed { var copy = ""; for (var i = 0; i < str.length; i++) { if ((str.charAt(i) >= "A" && str.charAt(i) <= "Z") || (str.charAt(i) >= "a" && str.charAt(i) <= "z")) { copy += str.charAt(i); } } return copy; suppose we want to test whether a word or phrase is a palindrome noon Radar Madam, I'm Adam. A man, a plan, a canal: } function isPalindrome(str) // Assumes: str is a string // Returns: true if str is a palindrome, else false { str = strip(str.toUpperCase()); for(var i = 0; i < Math.floor(str.length/2); i++) { if (str.charAt(i) != str.charAt(str.length-i-1)) { return false; } } return true; } Panama! must strip non-letters out of the word or phrase make all chars uppercase in order to be case-insensitive finally, traverse and compare chars from each end docsity.com <html> <!–- COMP519 js09.html 11.10.2011 --> <head> <title>Palindrome Checker</title> <script type="text/javascript"> function strip(str) { // CODE AS SHOWN ON PREVIOUS SLIDE } function isPalindrome(str) { // CODE AS SHOWN ON PREVIOUS SLIDE } </script> </head> <body> <script type="text/javascript"> text = prompt("Enter a word or phrase", "Madam, I'm Adam"); if (isPalindrome(text)) { document.write("'" + text + "' <b>is</b> a palindrome."); } else { document.write("'" + text + "' <b>is not</b> a palindrome."); } </script> </body> </html> view page docsity.com • Arrays have predefined methods that allow them to be used as stacks, queues, or other common programming data structures. var stack = new Array(); stack.push("blue"); stack.push(12); // stack is now the array ["blue", 12] stack.push("green"); // stack = ["blue", 12, "green"] var item = stack.pop(); // item is now equal to "green" Arrays (cont.) var q = [1,2,3,4,5,6,7,8,9,10]; item = q.shift(); // item is now equal to 1, remaining // elements of q move down one position // in the array, i.e. q[0] equals 2 q.unshift(125); // q is now the array [125,2,3,4,5,6,7,8,9,10] q.push(244); // q = [125,2,3,4,5,6,7,8,9,10,244] docsity.com Date Object • String & Array are the most commonly used objects in JavaScript other, special purpose objects also exist • the Date object can be used to access the date and time to create a Date object, use new & supply year/month/day/… as desired today = new Date(); // sets to current date & time newYear = new Date(2002,0,1); //sets to Jan 1, 2002 12:00AM methods include: newYear.getYear() can access individual components of a date newYear.getMonth() newYear.getDay() newYear.getHours() newYear.getMinutes() newYear.getSeconds() newYear.getMilliseconds() docsity.com Date Example <html> <!–- COMP519 js11.html 16.08.2006 --> <head> <title>Time page</title> </head> <body> Time when page was loaded: <script type="text/javascript"> now = new Date(); document.write("<p>" + now + "</p>"); time = "AM"; by default, a date will be displayed in full, e.g., Sun Feb 03 22:55:20 GMT-0600 (Central Standard Time) 2002 can pull out portions of the date using hours = now.getHours(); if (hours > 12) { hours -= 12; time = "PM" } else if (hours == 0) { hours = 12; } document.write("<p>" + hours + ":" + now.getMinutes() + ":" + now.getSeconds() + " " + time + "</p>"); </script> </body> </html> the methods and display as desired here, determine if "AM" or "PM" and adjust so hour between 1-12 10:55:20 PM view page docsity.com navigator Object <html> <!–- COMP519 js14.html 16.08.2006 --> <head> <title>Dynamic Style Page</title> <script type="text/javascript"> if (navigator.appName == "Netscape") { document.write('<link rel=stylesheet '+ 'type="text/css" href="Netscape.css">'); } else { <!-- MSIE.css --> navigator.appName property that gives the browser name navigator.appVersion property that gives the browser version document.write('<link rel=stylesheet ' + 'type="text/css" href="MSIE.css">'); } </script> </head> <body> Here is some text with a <a href="javascript:alert('GO AWAY')">link</a>. </body> </html> a {text-decoration:none; font-size:larger; color:red; font-family:Arial} a:hover {color:blue} <!-- Netscape.css --> a {font-family:Arial; color:white; background-color:red} view page docsity.com User-Defined Objects • can define new objects, but the notation can be somewhat awkward simply define a function that serves as a constructor specify data fields & methods using this no data hiding: can't protect data or methods // COMP519 Die.js 11.10.2011 // // Die class definition //////////////////////////////////////////// define Die function (i.e., object constructor) function Die(sides) { this.numSides = sides; this.numRolls = 0; this.roll = roll; // define a pointer to a function } function roll() { this.numRolls++; return Math.floor(Math.random()*this.numSides) + 1; } initialize data fields in the function, preceded with "this" similarly, assign method to separately defined function (which uses this to access data) docsity.com Object Example<html> <!–- COMP519 js15.html 11.10.2011 --> <head> <title>Dice page</title> <script type="text/javascript" src="Die.js"> </script> </head> <body> <script type="text/javascript"> die6 = new Die(6); die8 = new Die(8); create a Die object using new (similar to String and Array) here, the argument to Die initializes numSides for that particular object each Die object has its own roll6 = -1; // dummy value to start loop roll8 = -2; // dummy value to start loop while (roll6 != roll8) { roll6 = die6.roll(); roll8 = die8.roll(); document.write("6-sided: " + roll6 + " " + "8-sided: " + roll8 + "<br />"); } document.write("<br />Number of rolls: " + die6.numRolls); </script> </body> </html> properties (numSides & numRolls) Roll(), when called on a particular Die, accesses its numSides property and updates its NumRolls view page docsity.com
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