2019-06-21

 var a = 1
      function fn1 () {
        function fn3 () {
          function fn2 () {
            console.log(a)
          }
          fn2()
          var a = 4
        }
        var a = 2
        return fn3
      }
      var fn = fn1()
      fn()

      var a = 1
      function fn1 () {
        function fn2 () {
        console.log(a)
        }
        function fn3 () {
          fn2()
          var a = 4
        }
        var a = 2
        return fn3
      }
      var fn = fn1()
      fn()