为什么我的号码在我的Javascript中没有定义?

Question

所以我有这个任务，我应该使用javascript显示输出…我的数字在javascript中一直显示未定义，尽管我定义了它。我犯了什么错误吗?我是javascript的新手。我们正在练习使用对象字面量。预览将要发生的事情

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}`;