var,let和const的作用域

(() => {
  var a = 'a';
  let b = 'b';
  const c = 'c';
  if (true) {
    var d = 'd';
    let e = 'e';
    const f = 'f';
    console.log(a, b, c, d, e, f);
  }
  console.log(a, b, c, d, e, f);
})();

var的作用域是整个函数块, let, const作用域是它们所在的代码块