警报框未打印变量值

Question

我正在学习JavaScript，并且现在正在使用函数，并且试图警告用户输入的内容，但是当我输入名字和姓氏以及电子邮件并按订阅时，警告框显示：

Hello [object HTMLInputElement] [object HTMLInputElement]! Your email [object HTMLInputElement] was succesfully registered ...

这是我的代码：

<script>
    function printMessage(firstNameID,lastNameID,emailID){
        var firstName = document.getElementById(firstNameID);
        var lastName = document.getElementById(lastNameID);
        var email = document.getElementById(emailID);
        alert("Hello " + firstName + " " + lastName + "! Your email " + email + " was succesfully registered ...");
    }
</script>
<form name="subscribeform">
    First Name: <br>
<input type="textbox" id="firstname" form="subscribeform"><br>
    Last Name: <br>
<input type="textbox" id="lastname" form="subscribeform"><br>
    Email: <br>
    <input type="textbox" id="email" form="subscribeform"><br><br>
    <button id="subscribe" form="subscribeform" onclick="printMessage('firstname','lastname','email');">Subscribe, you know you want to ...</button>
    </form>

Answer 1

您需要元素的value ，而不是元素本身。

alert("Hello " + firstName.value + " " + lastName.value + "! Your email " + email.value + " was succesfully registered ...");

要么...

var firstName = document.getElementById(firstNameID).value;
var lastName = document.getElementById(lastNameID).value;
var email = document.getElementById(emailID).value;