howBabelTakesCaseOflet.js

// Say you have this function
function demo() {
  var a = 1;
  let b = 2;
  if (1) {
    var c = 3;
    let d = 4;
    console.log(a, b, c, d);
  }
  console.log(a, b, c, d);
}
// if we execute demo() it will give a ReferenceError: d is not defined. This is because d being defined by let wont be available
// outside the scope of if. If we define it with var it works fine. How does babel make us get this reference error for the first case?

// We need to define the block within an IFFE

// This works fine
function demo() {
  var a = 1;
  let b = 2;
  if (1) {
    var c = 3;
    var d = 4;
    console.log(a, b, c, d);
  }
  console.log(a, b, c, d);

  // This will give e refereence error for d as it would give if d was defined with let.

  function demo() {
    var a = 1;
    let b = 2;
    if (1) {
      var c = 3;
      (function() {
        var d = 4;
        console.log(a, b, c, d);
      })();
    }
    console.log(a, b, c, d);
  }
}