ES6 Variables

ES6 Variables

 

 

Now, with ES6, there are three keywords available to define variables: They provide different levels of scope to access the variable. Based on the requirement, you can define variables with these keywords and control its accessibility.

• var 
  
• let
• const

 

Using ES6 var

Example

var x = 9.9;

If var declared outside a function, it belongs to the global scope.

If var declared inside a function, it belongs to that function.

If var declared inside the block, ex: in a for loop, the variable is still available outside that block.

var has a function scope, not a block scope. 

Using ES6  let

Example

 

let x = 9.9;

let is the block scoped version of var, and is limited to the block, where it is defined.

If you use let inside a block, i.e. a for loop, the variable is only available inside that loop.

let has a block scope.

Using ES6 const

Example

const  y = 9.9;

 y=10;   // It will result in an error  
 

constant is a read only variable. Once it is initialized, it cannot be changed.

const has a block scope.
 
Actually It defines a constant reference to a value, not
not define a constant value.

With this reason, you can NOT Reassign:

    a constant value
    a constant array
    a constant object

    But you CAN change:
    the elements of constant array and
    the properties of constant object