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How To Declare Variables in JavaScript?

Variables can be thought of as named containers. You can place data into these containers and then simply refer to the data 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 xyz;
var abc123;
var stu_dent; 
</script>

The scope of a variable is the region of your program in which it is defined. JavaScript variable will have only two scopes:
  • Global Variables: A global variable has global scope which means it is defined everywhere 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.

While naming variables in JavaScript keep following rules in mind:
  • You should not use any of the JavaScript reserved keyword as variable name. 
  • Variable names should not start with a numeral (0-9). They must begin with a letter or the underscore character. For example, 123test is an invalid variable name but _123test is a valid one.
  • Variable names are case sensitive. For example, Name and name are two different variables.

 The following are reserved words in JavaScript. They cannot be used as variables, functions, methods, loop labels, or any object names.

abstract
boolean
break
byte
case
catch
char
class
const
continue
debugger
default
delete
do
double
else
enum
export
extends
false
final
finally
float
for
function
goto
if
implements
import
in
instanceof
int
interface
long
native
new
null
package
private
protected
public
return
short
static
super
switch
synchronized
this
throw
throws
transient
true
try
typeof
var
void
volatile
while
with

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