Using OAuth 2.0 Authorization framework

JavaScript

JavaScript is fun and powerful programming language for front end  web developing.  JavaScript is used most of the popular web applications. Eg : google Map , Gmail , PayPal , LinkedIn …… etc.

JavaScript Variable Type

JavaScript is loosely type language. In variable declaration we don’t need to define any datatype like integer, string , Boolean. We can declare  all type of variable not only integer, Boolean , string but also objects  just using ‘var’ or ‘let’ or ‘const’ keywords.

Later we’ll discuss about different between these above mentioned keyword. But commonly we use var keyword to declare variable.

Variable declaration 

When declare a variable without initializing a value then it will automatically take undefined  or null value. And also we can define multiple variable with same var keyword.

Variable naming concerns.

1. JavaScript is case – sensitive.  eg : Age , age are two different variable.
2. We can’t use JavaScript key word eg: int , let , break , class , export , supper , final.
3. Variable name should not start with numbers(0-9) , must begin with a letter or underscore or dollar sign

               Eg:  1name   == invalid

                              _12name is valid

Variable scope

In javascript there are two types of variable scope

       1.Global Variable

       2.Local Variable

Global variable

These variables are define out of the function scope. All global variables are belongs to the window object. For best practice these global variables are define in uppercase letters.

Global variables can be got from anywhere.

         

If we declare a variable without ‘var’ keyword it will automatically assign as global variable.

         

Local variable

Local variables are define inside the function. These variables only accessible within that function. 

   
     

       

 Var , let , const

• Var keyword used to define a variable within the functional scope. Let and const keyword used to define a variable within the block scope. 

         

       

• Var & let variables can change their value but const variables can’t change.
• Const variable can’t be declared without initialization but var and let not like that.

       

• Duplicate declaration of variable is possible with var but not possible in let and const.