SOURCE

  console.log('a = ', a); // a = undefined
  console.log('fun = ', fun);
  fun();
//   fun2();
  var a = 1; 
  function fun(){
    console.log('我是fun');
  }
  var fun2 = function () {
    console.log('我是fun2');
  }
  function func6(e){
    // 相当于定义了 var e;
    console.log(e); // undefined
  }
  func6();