我想使用该值调用对象实例

Question

我有一个JavaScript代码，可显示列表中某人的姓名和年龄。但是为了调用正确的事件，我需要将下拉列表值传递给要创建的新变量和对象。

在button1下面的相同代码中，按字符串不能正常工作。但是按钮2。

function Person(first, last, age, eye) {
  this.firstName = first;
  this.lastName = last;
  this.age = age;
  this.eyeColor = eye;
}

var myF = new Person("John", "Doe", 50, "blue");
var myM = new Person("Sally", "Rally", 48, "green");

function test1() {
  var per = document.getElementById("peep").value;
  document.getElementById("demo").innerHTML = per.firstName + " is " + per.age + " years old"
}

function test2() {
  var met = document.getElementById("peep").value;
  var mat = document.getElementById("att").value;

  //making objects of dropdown values
  if (met == "myF") {
    var per = myF
  } else if (met == "myM") {
    var per = myM
  };

  document.getElementById("demo").innerHTML = per[mat] + " is " + per.age + " years old"

}

<h2>JavaScript Objects</h2>
<select id="peep" name="people">
  <option value="myM">mom</option>
  <option value="myF">dad</option>
</select>
<select id="att" name="atributes">
  <option value="firstName">first</option>
  <option value="lastName">last</option>
</select>
<br>
<input type="button" value="Button 1" onclick="test1()">
<input type="button" value="Button 2" onclick="test2()">
<br/>
<p id="demo"></p>

Answer 1