Variables in JavaScript
Variables in javascript: A javascript is simply a name of storage location, variables are case sensitive, there are three types of variables in javascript
- Var
- Let
- Const
Var: a Variables is an identifier or a name which a user to refer a value
Syntax:
Var <Variable-name>; Var <Variable-name>=value;
Example:
<!DOCTYPE html> <html> <body> <script> var FirstName="Programming master"; document.write(FirstName); </script> </body> </html>
Output:
Programming master
Example:
<!DOCTYPE html> <html> <body> <script> var x="Programming master"; document.write(x); document.write(x); document.write(x); </script> </body> </html>
Output:
Programming master
Programming master
Programming master
Example:
Override variable value
<!DOCTYPE html> <html> <body> <script> var FirstName="Programming master"; FirstName="JavaScript"; document.write(FirstName); </script> </body> </html>
Or
<!DOCTYPE html> <html> <body> <script> var FirstName="Programming master"; var FirstName="JavaScript"; document.write(FirstName); </script> </body> </html>
Output: JavaScript
- Let : in let once we declare a variable name, we cannot declare same variable name again and again otherwise it will give an error
Example :
<!DOCTYPE html> <html> <body> <script> let FirstName="Programming master"; document.write(FirstName); </script> </body> </html>
Output:
Programming master
Example:
<!DOCTYPE html> <html> <body> <script> let FirstName="Programming master"; FirstName="JavaScript"; document.write(FirstName); </script> </body> </html>
Output : JavaScript
Example:
Error : Identifier ‘FirstName’ has already been declared
<!DOCTYPE html> <html> <body> <script> let FirstName="Programming master"; let FirstName="JavaScript"; document.write(FirstName); </script> </body> </html>
- Const: once you declare a variable name and you assign a value to that variable name you cannot reassign name and value
Example:
<!DOCTYPE html> <html> <body> <script> const FirstName="Programming master"; document.write(FirstName); </script> </body> </html>
Output:
Programming master
Example: Error Assignment to constant variable
<!DOCTYPE html> <html> <body> <script> const FirstName="Programming master"; const FirstName="JavaScript"; document.write(FirstName); </script> </body> </html>
Example :Error Identifier FirstName has already been declared
<!DOCTYPE html> <html> <body> <script> const FirstName="Programming master"; const FirstName="JavaScript"; document.write(FirstName); </script> </body> </html>