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JavaScript

JavaScript. Scripting language. What is Scripting ?. A scripting language, script language, or extension language is a programming language that allows control of one or more applications.

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JavaScript

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  1. JavaScript Scripting language IT @YCCE 2011-12

  2. What is Scripting ? • A scripting language, script language, or extension language is a programming language that allows control of one or more applications. • Scripts are often interpreted from source code or bytecode, whereas the application is typically first compiled to native machine code. IT @YCCE 2011-12

  3. What is Client Side Scripting ? Client Side Scripting: • Client-side scripting generally refers to the class of computer programs on the web that are executed client-side, by the user's web browser, instead of server-side (on the web server). IT @YCCE 2011-12

  4. Client-Side Scripting Languages • Netscape and others • JavaScript • Internet Explorer • Jscript (MS name for JavaScript) • VBScript • PerlScript IT @YCCE 2011-12

  5. What is JavaScript • JavaScript was designed to add interactivity to HTML pages • JavaScript is a scripting language (a scripting language is a lightweight programming language) • A JavaScript consists of lines of executable computer code • A JavaScript is usually embedded directly into HTML pages • JavaScript is an interpreted language (means that scripts execute without preliminary compilation) • Everyone can use JavaScript without purchasing a license IT @YCCE 2011-12

  6. Why do we use JavaScript ? • Add content to a web page dynamically. • Alter a web page in response to user actions. • React to user events. • Interact with frames. • Manipulate HTTP cookies IT @YCCE 2011-12

  7. Features • Browser support • Detecting user’s browser and OS • Can be used on Server as well as Client • Performing simple Computation • Support objects IT @YCCE 2011-12

  8. Structure of JavaScript program <html> <head> <title>JavaScript Page</title> <script language="javascript"> document.write("Hello world!"); </script> </head> <body> Content of the Page </body> </html> IT @YCCE 2011-12

  9. JavaScript andHTML Comments <SCRIPT> <!-- document.write(“Hello World"); --> </SCRIPT> HTML comment IT @YCCE 2011-12

  10. Language Elements • Variables • Literals • Operators • Control Structures • Objects • Arrays IT @YCCE 2011-12

  11. Variables • Untyped! • Can be declared with var keyword: varfoo; • Can be created automatically by assigning a value: foo=1; blah="Hi Dave"; IT @YCCE 2011-12

  12. Variables (cont.) • Using var to declare a variable results in a local variable (inside a function). • If you don't use var – the variable is a global variable. IT @YCCE 2011-12

  13. Literals(Values) • Values are bits of information. • Values types and some examples include: • Number: 1, 2, 3, etc. • String: characters enclosed in quotes. “Hi” • Boolean: true or false. • Object: image, form • Function: validate(), doWhatever() IT @YCCE 2011-12

  14. Expressions • Expressions are commands that assign values to variables. • Expressions always use an assignment operator, such as the equals sign. • e.g., var month = May; is an expression. • Expressions end with a semicolon. IT @YCCE 2011-12

  15. Operators • Arithmetic, comparison, assignment, bitwise, boolean (pretty much just like C). + - * / % ++ -- == != > < && || ! & | << >> IT @YCCE 2011-12

  16. Control Structures • Again – pretty much just like C: if if-else ?: switch for while do-while • And a few not in C for (var in object) with (object) IT @YCCE 2011-12

  17. Function function functionname (Parameter list) { Commands; return value; } • The two parts of a JavaScript function are ✦ Parameter list: Defines any data and their data types that the function needs to work. If the function doesn’t need to accept any values, the parameter list can be empty. • ✦ Return: Defines a value to return. IT @YCCE 2011-12

  18. User-defined functions • function definitions are similar to C++/Java, except: • no return type for the function (since variables are loosely typed) • no types 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) { return false; } else if (n == 2) { return true; } else { for (vari = 2; i <= Math.sqrt(n); i++) { if (n % i == 0) { return false; } } return true; } } can limit variable scope if the first use of a variable is preceded with var, then that variable is local to the function for modularity, should make all variables in a function local IT @YCCE 2011-12

  19. Embedding JavaScript in HTML. • When specifying a script only the tags <script> and </script> are essential, but complete specification is recommended: <script language="javascript” type="text/javascript"> <!-- Begin hiding window.location=”index.html" // End hiding script--> </script> IT @YCCE 2011-12

  20. Objects • Objects have attributes and methods. • Many pre-defined objects and object types. • Using objects follows the syntax of C++/Java: objectname.attributename objectname.methodname() IT @YCCE 2011-12

  21. Array Objects • Arrays are supported as objects. • Attribute length • Methods include: Concat() join() pop() push() reverse() sort() IT @YCCE 2011-12

  22. Array example code var a = [8,7,6,5]; for (i=0;i<a.length;i++) a[i] += 2; b = a.reverse(); IT @YCCE 2011-12

  23. Many other pre-defined object types • String: manipulation methods • Math: trig, log, random numbers • Date: date conversions • RegExp: regular expressions • Number: limits, conversion to string IT @YCCE 2011-12

  24. Alert Box • An alert dialog box displays a message on the screen and gives the user the option of closing the dialog box. • To create an alert dialog box, you need to define the text you want displayed, such as alert(“Message here”); • An alert dialog box displays an OK button. As soon as the user clicks this OK button, the alert dialog box goes away. IT @YCCE 2011-12

  25. Confirmation Box • A confirmation dialog box displays a message and offers the user two or more choices. • A confirmation dialog box gives users a choice of OK and Cancel buttons. • To create a confirmation dialog box, you must display text and include commands that do something when the user clicks either OK or Cancel: if (confirm(“Text message”)) command; else command; IT @YCCE 2011-12

  26. Prompt Box • A prompt dialog box gives users a chance to type in data. • To create a prompt dialog box, you need to display text to appear in the dialog box and then optional text to appear as a default value, such as • prompt(“Text to display”, optionalvalue); IT @YCCE 2011-12

  27. Simple program using JavaScript <html> <head> <script language=javascript> <!-- function hello() { document.write("Hello,This is JavaScript Output"); } --> </script> </head> <body onLoad ="hello()"> </body> </html> IT @YCCE 2011-12

  28. Queries ?? IT @YCCE 2011-12

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