为什么我的 Javascript 中的号码没有定义？

Question

所以我有这个任务，我应该使用 javascript 显示输出... 即使我定义了它，我的号码仍然在 javascript 中显示未定义。我犯了一个错误吗？我是 JavaScript 新手。我们正在练习使用对象字面量。 preview of what is supposed to happen

function displayStudent() {
   
    student = {
        firstname: "",
        lastname: "",
        number: 0
        }
        
    student.firstname = document.getElementById("firstname").value;
    student.lastname = document.getElementById("lastname").value;
    student.number = document.getElementById("studentnumber").value;

    display = `${firstname}, ${lastname}, ${number}`;

    document.getElementById("studentinfo").innerHTML = display;

}

<fieldset>
        <legend>Input Area</legend>  
        <br><br>
        <label for="week">Week Number:</label>
        <input type="number" id="week" maxlength="2" size="2" value="0"> 
        <label for="fname">First name:</label>
        <input type="text" id="firstname" name="fname">  
        <label for="lname">Last name:</label>
        <input type="text" id="lastname" name="lname">   
        <label for="studentnumber">Student Number:</label>
        <input type="number" id="studentnumber" name="number">  
          
        <button id = "button">Generate Lotto Tickets</button>
   </fieldset>

   <fieldset>

    <legend id="display">Display Area</legend>  
    <label for="title">Module Title:</label>
        <output id="wTitle"><i>module title</i></output><br><br>
    <label for="fname">Student info:</label>
        <output id="studentinfo"><i>Student info</i></output>
    <label for="date">Current Date:</label>
        <output id="cdate"><i>Current Date</i></output>
     


    </fieldset>

Answer 1

将display = `${firstname}, ${lastname}, ${number}`; 替换为display = `${student.firstname}, ${student.lastname}, ${student.number}`;