Java script
- 1. BY G.GOWRILATHA,M.Sc(Info Tech) Department Of CS & IT Nadar Saraswathi College Of Arts and Science, Theni.
- 2. JavaScript is a lightweight, interpreted programming language. It is designed for creating network-centric applications. It is complimentary to and integrated with Java. JavaScript is very easy to implement because it is integrated with HTML. It is open and cross-platform.
- 3. Java script is a dynamic computer programming language. It is lightweight and most commonly used as a part of web pages, whose implementations allow client-side script to interact with the user and make dynamic pages. It is an interpreted programming language with object-oriented capabilities. JavaScript was first known as Live Script, but Netscape changed its name to JavaScript, possibly because of the excitement being generated by Java.
- 4. Client-side JavaScript is the most common form of the language. The script should be included in or referenced by an HTML document for the code to be interpreted by the browser. It means that a web page need not be a static HTML, but can include programs that interact with the user, control the browser, and dynamically create HTML content. The JavaScript client-side mechanism provides many advantages over traditional CGI server-side scripts. For example, you might use JavaScript to check if the user has entered a valid e-mail address in a form field.
- 5. Less server interaction: you can validate user input before sending the page off to the server. This saves server traffic, which means less load on your sever. Immediate feedback to the visitors: They don’t have to wait for a page reload to see if they have forgotten to enter something. Increased Interactivity: you can create interface that react when the user hovers over them with a mouse or activates them via the keyboard. Richer interface: you can use java Script to include such items as drag-and-drop components and sliders to give arch interface to your site visitors.
- 6. The <script> tag alerts the browser program to start interpreting all the text between these tags as a script. The script tag takes two important attributes: Language: This attribute specifies what scripting language you are using. Typically, its value will be java script. Type: This attribute is what is now recommended to indicate the scripting language in use and its value should be set to "text/java script". <script ...> JavaScript code </script>
- 7. Java Script allows you to work with three primitive data types: Numbers, eg.,123,120.50 etc. Strings of text , eg. “This text String” etc. Boolean, eg. True or false. Java Script also defines two trivial data types, null and undefined, each of which defines only a single value. In addition to these primitive data types, JavaScript supports a composite data type known as object. ,
- 8. Like many other programming languages, JavaScript has variables. Variables can be thought of as named containers. You can place data into these containers and then refer to the data simply by naming the container. Before you use a variable in a JavaScript program, you must declare it. Variables are declared with the var keyword as follows. <script type=“text/javascript”> <!— Var money; Var name; //--> </script>
- 9. The scope of a variable is the region of your program in which it is defined. JavaScript variables have only two scopes. Global Variables: A global variable has global scope which means it can be defined anywhere in your JavaScript code. Local Variables: A local variable will be visible only within a function where it is defined. Function parameters are always local to that function. Within the body of a function, a local variable takes precedence over a global variable with the same name.
- 10. While naming your variables in JavaScript, keep the following rules in mind. You should not use any of the JavaScript reserved keywords as a variable name. These keywords are mentioned in the next section. For example, break or Boolean variable names are not valid. JavaScript variable names should not start with a numeral (0-9). They must begin with a letter or an underscore character. For example, 123test is an invalid variable name but _123test is a valid one. JavaScript variable names are case-sensitive. For example, Name and name are two different variables.
- 11. •There are three special values in JavaScript that are considered numbers but •don’t behave like normal numbers. •The first two are Infinity and -Infinity, which represent the positive and negative infinities. Infinity - 1 is still Infinity, and so on. Don’t put too much trust in infinity-based computation, though. It isn’t mathematically sound, and it will quickly lead to the next special number: NaN. •NaN stands for “not a number”, even though it is a value of the number type. •You’ll get this result when you, for example, try to calculate 0 / 0 (zero divided by zero), Infinity - Infinity, or any number of other numeric operations that don’t yield a meaningful result.
- 12. The next basic data type is the string. Strings are used to represent text. They are written by enclosing their content in quotes. `Down on the sea` "Lie on the ocean" 'Float on the ocean' You can use single quotes, double quotes, or back ticks to mark strings, as long as the quotes at the start and the end of the string match.