scope.js

var baz = 'yes';
if (true) {
  var baz = 'no';
}
console.log(baz); // 'no'

let bar = 'yes';
if (true) {
  let baz = 'no';
}
console.log(baz); // 'yes'

let foo = 'yes';
let foo = 'no'; // SyntaxError: 'foo' has already been declared

for (var i = 0; i < 4; i++) {
  baz[i] = True;
}
console.log(i); // 4

for (let j = 0; j < 4; j++) {
  baz[j]  = False;
}
console.log(j); // ReferenceError: j is not defined