2022-02-15 块级作用域

function foo(){

  var a = 1

  let b = 2

  {

    let b = 3

    var c = 4

    let d = 5

    console.log(a)

    console.log(b)

  }

  console.log(b)

  console.log(c)

  console.log(d)

}

foo()