Why not to use var in variable declaration, and instead use let or const in JavaScript

test-var-let-const.js

// Global Scope
var a = 1;
var b = 2;
var c = 3;

// Testing Block Scope
if(true) {
  // Block scope
  var a = 4;
  let b  = 5;
  const c = 6;
  console.log('If Scope: ', a, b, c);
}

console.log('Global Scope: ', a, b, c);

// Output will be as follows
// Block Scope of if Statement: 4, 5, 6
// Global Scope: 4, 2, 3