var or const javascript code example

Example 1: javascript var let

// var has function scope.
// let has block scope.

function func(){
  if(true){
    var A = 1;
    let B = 2;
  }
  A++; // 2 --> ok, inside function scope
  B++; // B is not defined --> not ok, outside of block scope
  return A + B; // NaN --> B is not defined
}

Example 2: what is const in javascript

const age; // errror as const cannot be kept un-initialized;
const age = 20 ; 
const age = 21 , // error as once declared const variable cann't be
// re-declared in same scope or different scope.

Example 3: var or const in javascript

// var declares a variable, meaning its value will vary. 
// const declares a constant, meaning its value will remain 
// consistant and not change. 
// If your variable changes throughout the program or website, 
// declare it using a var statement. 
// Otherwise, if its value does not change, declare it using 
// a const statement. 

const myConst='A const does not change.';

var myVar='A var does change.';

var myVar=2;