Денис Инешин

if (true) {
  var foo = 'bar';
}

console.log(foo); // bar

if (true) {
  var foo = 'bar';
  let baz = 'biz';
  const alpha = 'beta';
}

console.log(foo); // bar
console.log(baz); // ReferenceError: baz is not defined
console.log(alpha); // ReferenceError: alpha is not defined

if (true) {
  const foo = () => {};
}

console.log(foo); // ReferenceError: foo is not defined

function foo () {
  function bar() {}
}

console.log(bar); // ReferenceError: bar is not defined

const arr = [
  ['a', 1],
  ['b', 2],
  ['c', 3],
];

const map = new Map(arr);
// Map { 'a' => 1, 'b' => 2, 'c' => 3 }

const arr = [
  ['a', 1],
  ['b', 2],
  ['c', 3],
  ['b', 99],
];

const map = new Map(arr);
// Map { 'a' => 1, 'b' => 99, 'c' => 3 }