分析函数的参数是引用类型的数据

 修改对象属性，会影响person

      function setName(obj) {
        obj.name = 'Nicholas'
        console.log(obj.name)  //Nicholas
        //obj = {}
        obj.name = 'Greg'
        console.log(obj.name)  //Greg
      }
      let person = {}
      setName(person)
      console.log(person.name) //Greg

 给引用类型的数据赋值新对象后，person依然指向旧对象，obj指向新对象，person就像一把钥匙，打开的房间是旧房间，obj已经是新钥匙了

      function setName(obj) {
        obj.name = 'Nicholas'
        console.log(obj.name)  //Nicholas
        obj = {}
        obj.name = 'Greg'
        console.log(obj.name)  //Greg
      }
      let person = {}
      setName(person)
      console.log(person.name) //Nicholas

 赋值新数组是类似的

      function setName(obj) {
        obj.name = 'Nicholas'
        console.log(obj.name)  //Nicholas
        obj = []
        obj[0] = 'Greg'
        console.log(obj[0])  //Greg
      }
      let person = {}
      setName(person)
      console.log(person.name) //Nicholas