Javascript Variables and Values:
Javascript Variables
Variables are the
basic fundamental building blocks of JavaScript expressions. Variables can store
and retrieve data. A variable is a symbolic name that represents some data that you set. A variable can be referred by a name. Certain rules apply
when you create a variable name.
A JavaScript identifier
or name:
must start with
a letter or underscore ("_")
subsequent characters
can also be digits (0-9)
Examples : myname, address1,address2,_zipcode are examples
for variable names.
When using a variable for the first time it is not necessary to use "var" before the variable name, but it is a good programming practice to make it crystal clear when a variable is being used for the first time in the program.Please remember
that JavaScript is case sensitive. This means that variables Myname and
myname are different variables even though both have same names.
Javascript - Declaring
variables
A Javascript variable
can be declared in two ways:
By assigning
the variable a value; Eg: myname = "Bob";
By using keyword
var; for example, var myname = "Bob";
Variable Scope
:
A variable may be have a either global or local scope.
Global variable
:A global variable is available everywhere in the current document In
addition you can access global variables declared in one window or frame from
another window or frame by specifying the window or frame name.
Usually a new global variable is created by assigning it a value:
Eg:
<script>
// Example for Global variable
var globalVar1 = "Test value for global variable";
function
ExampleForLocalvariable() {
var LocalVar1 = "Test value for local
variable";
alert(LocalVar1);
}
alert(globalVar1);
</script>
Local Variable
: A local variable is available only within the function where it was
assigned. To create a local variable which has a scope within a function,
the new variable should be declared using the var statement:
Eg:
<script>
var globalVar1 = "Test value for global variable";
function
ExampleForLocalvariable() {
// Example for local variable
var LocalVar1 = "Test value for
local variable";
alert(LocalVar1);
}
alert(globalVar1);
</script>
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Javascript - Data Types:
Every Javascript variable can be assigned a value. The value assigned could
be a string or a number. JavaScript recognizes the following data types :
| Integers |
Integers can be positive, 0, or negative;
Integers can be expressed in decimal (base 10), hexadecimal (base 16),
and octal (base 8). A decimal integer literal consists of a sequence of
digits without a leading 0 (zero). A leading 0 (zero) on an integer literal
indicates it is in octal; a leading 0x (or 0X) indicates hexadecimal.
Hexadecimal integers can include digits (0-9) and the letters a-f and
AF Octal integers can include only the digits 0-7.
Some examples of integer literals
are: 24 0xFFF, and -435.
|
| Floating-point number |
A floating-point number can have
the following parts:
1)a decimal integer
2)a decimal point (".")
3)a fraction (another decimal number)
4)an exponent
5)a type suffix
The exponent part is an "e" or "E"
followed by an integer, which can be signed (preceded by "+" or "-").
A floating-point literal must have at least one digit and either a decimal
point or "e" (or "E").
Some examples of floating-point literals
are 3.1415, -3.1E12, .1e12, and 2E-12
|
| Boolean |
True or False. The possible
Boolean values are true and false. These are special values, and are not
usable as 1 and 0. In a comparison, any expression that evaluates to 0
is taken to be false, and any statement that evaluates to a number other
than 0 is taken to be true. |
| Strings |
"Hello !" Strings are delineated
by single or double quotation marks. (Use single quotes to type strings
that contain quotation marks.) |
| Objects |
myObj = new Object(); |
| null |
Not the same as zero - no value
at all. A null value is one that has no value and means nothing. Because
JavaScript is case sensitive, null is not the same as Null, NULL, or any
other variant. |
| Undefined |
A value that is undefined is a value
held by a variable after it has been created, but before a value has been
assigned to it. |
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Javascript - Data Type Conversion
Javascript is a
NOT a strongly typed language. While declaring a new variable, you do not have
to specify the data type of a variable. Data types are converted automatically
as needed during script execution.
For example, you
could define a variable as follows:
var myvar=20
Later in your script, you may assign the same variable myvar a string
value, for example,
myvar = "Welcome
home!!"
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Javascript - Special Characters :
| Character |
Meaning |
| \b |
backspace |
| \f |
form feed |
| \n |
new line |
| \t |
tab |
| \\ |
backslash character |
| \r |
carriage return |
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