测试题

  function a() {}
  var a;
  console.log(typeof a) //function

  if (!(b in window)) {
    var b = 1;
  }
  console.log(b) // undefined

  var c = 1
  function c(c) {
    console.log(c)
    var c = 3
  }
  c(2) // c is not a function