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Chapter: 11th Computer Applications : Introduction to JavaScript

JavaScript Variables

Variable is a memory location where value can be stored. Variable is a symbolic name for a value.

JavaScript Variables:

 

Variable is a memory location where value can be stored. Variable is a symbolic name for a value. Variables are declared with the var keyword in JavaScript. Every variable has a name, called identifier.

 

Basic Data types and Declaring variables:

 

Every variable has a data type that indicates what kind of data the variable holds. The basic data types in JavaScript are Strings, Numbers, and Booleans.

         A string is a list of characters, and a string literal is indicated by enclosing the characters in single or double quotes. Strings may contain a single character or multiple characters, including whitespace and special characters such as \n (the newline).

         Numbers can be integer or floating-point numerical value and numeric literals are specified in the natural way.

         Boolean can be any one of two values: true or false. Boolean literals are indicated by using true or false directly in the source code.

Variables are declared in JavaScript using var keyword that allocates storage space for new data and indicates to the interpreter that a new identifier is in use. Declaring a variable in JavaScript as follows:

var no;

var no1,no2;

The var no; statement tells the interpreter that a new variable no is about to be used and var no1,no2; tells the interpreter that no1 and no2 are variables.

 

Rules for naming variable

 

1.     The first character must be a letter or an underscore (_). Number cannot be as the first character.

2.     The rest of the variable name can include any letter, any number, or the underscore. You can't use any other characters, including spaces, symbols, and punctuation marks.

3.     JavaScript variable names are case sensitive. That is, a variable named RegisterNumber is treated as an entirely different variable than one named registernumber.

4.     There is no limit to the length of the variable name.

5.     JavaScript's reserved words cannot be used as a variable name. All programming languages have a supply of words that are used internally by the language and that cannot be used for variable names.

 

Scope of variables

 

The scope of a variable is the life time of a variable of source code in which it is defined.

         A global variable has global scope; it can be defined everywhere in the JavaScript code.

         Variables declared within a function are defined only within the body of the function. They are local variables and have local scope.

 

Assigning values to variables

 

Variables can be assigned initial values when they are declared as follows:

var numericData1 = 522;

var stringData = "JavaScript has strings\n It sure does";

var numericData = 3.14;

var booleanData = true;

 

Illustration 14.2 Declaring Variables

<Html>

<Head>

        <Title>Demo Program - Declaring Variables in JavaScript </Title>

</Head>

<Body>

<script language="javascript" type="text/javascript">

        var numericData1 = 522;

        var stringData = " JavaScript has strings\n It sure does";

        var numericData = 3.14;

        var booleanData = true;

        document.write("Numeric Data : "+numericData1);

        document.write("<br> String Data  :  "+stringData);

        document.write("<br> Floating Data : "+numericData);

</script>

</Body>

</Html>

Output


In addition, multiple variables can be declared with one var statement, if the variables are separated by commas:

var no1=50, no2=5065;

JavaScript allows the implicit declaration of variables by using them on the left-hand side of an assignment. In JavaScript there is no need to indicate data type during variable declarations. JavaScript variables are untyped and it is dynamically datatyped which means initially you can assign a value of any data type to a variable and later you can assign a value of different data type to the same variable. For example:

var value=100;

var value=”JavaScript”;

 

JavaScript Literals

 

A literal is a fixed value given to a variable in source code. Literals are often used to initialize variables. Values may be Integer, Floating point, Character, String and Boolean. For Example,

var int_const=250; //Integer constant//

var float_const=250.85; //Floating point constant//

var char_const=’A’; //Character constant//

var string_const=”Raman”; //String constant//

var boolean_const=true; //Boolean constant//

write statement:

General Syntax:

document write ("string " + var);

 

Type casting in JavaScript.

 

Type conversion is the act of converting one data type into a different data type which is also called as casting. In JavaScript there are two type of casting,

         Implicit casting and

         Explicit casting

Implicit casting occurs automatically in JavaScript when you change the data stored in a variable:

 

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11th Computer Applications : Introduction to JavaScript : JavaScript Variables |


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