为什么我的异常处理没有捕获

Question

这是我试图创建异常处理的html代码。我正在尝试为这段代码中的第一个表单创建异常。

<form id="survey" name="survey" method="post">
<div id="errorText"></div>
<fieldset class="labelfloatleft" id="contactinfo"><legend>Your Thoughts</legend>
<label for="firstname">First Name</label>
<input type="text" name="firstname" id="firstname" />
<label for="lastname">Last Name</label>
<input type="text" name="lastname" id="lastname"  />
<label for="emailaddress">Email Address</label>
<input type="email" name="emailaddress" id="emailaddress" 
size="30" placeholder="[e-mail]" />
</fieldset>
<fieldset><legend>Best Movie</legend>
<input type="radio" name="movie" id="horror" value="horror" checked="checked"/>
<label for="horror">The Horror</label>
<input type="radio" name="movie" id="badabing" value="badabing" />
<label for="badabing">Bada-Bing Bada-Boom</label>
<input type="radio" name="movie" id="roll" value="roll" />
<label for="roll">Roll or Die</label>
</fieldset>
<fieldset><legend>Comments</legend>
<label for="message">Your Opinion</label>
<textarea name="message" id="message" rows="7" cols="30"></textarea>
</fieldset>
<input type="submit" value="Send" class="button" id="submitBtn"/>
<input type="reset" value="Cancel" class="button" />
</form>

<h2>Welcome To Our World</h2>
<p class="very">We are a small time movie theater looking to help inspire
people who come to our theater. Our theaters come with
fresh food, cold and hot drinks, souvenirs and comfortable
seats to help make your experience worth while.
</p>
<h2>Most Popular</h2>
<ul>
<li>The Horror</li> 
<li>Bada-Bing Bada-Boom</li> 
<li>Roll or Die</li>
</ul>

<h2>Prices</h2>
<table title="prices">
<tr>
<th>Ticket</th>
<th>Price</th>
<th>Thursday Deal</th>
</tr>
<tr>
<td>Adult</td>
<td>$10.00</td>
<td rowspan="3">Half-Off</td>

</tr>
<tr>
<td>Child</td>
<td>$6.00</td>
</tr>
<tr>
<td>Senior</td>
<td>$8.00</td>
</table>
<form id="price" name="price" method="post">
<fieldset><legend>Ticket Quantity</legend>
<label for="adultinput">Adult 15-60
<input type="text" id="adultinput" value="1" size="2"/>
</label>
<label for="childinput">Child 1-14
<input type="text" id="childinput" value="0" size="2"/>
</label>
<label for="seniorinput">Senior 50 and up
<input type="text" id="seniorinput" value="0" size="2"/>
</label>
</fieldset>
<input type="submit" value="Calculate" id="calculate" class="button" />
<input type="reset" value="Cancel" class="button" />
</form>

这是我正在尝试使用的异常处理代码。然而，无论我如何修改它，它都不会正确显示。我已经在Chrome中运行了它，并尝试使用调试器来提供帮助，但当我单击提交按钮时，我仍然无法显示异常。

"use strict";
var fnameComplete = true;
var lnameComplete = true;
var emailComplete = true;
var fname = document.getElementById("firstname").value;
var lname = document.getElementById("lastname").value;
var email = document.getElementById("emailaddress").value;
var errorDiv = document.getElementById("errorText");
function verifyFname() {
var validity = true;    
var messageText = "";
var errorDiv = document.getElementById("errorText");
try {
if(!(isNaN(fname.value)) || (fname.value === "")){
fname.style.background = "rgb(255,233,233)";
throw "Please enter your first name.";
} 
}
catch(message) {
validity = false;
messageText = message;
}
finally{
numErrorDiv.style.display = "block";
fnameComplete = validity;
errorDiv.innerHTML = messageText;
}
}
function verifyLname() {
var validity = true;    
var messageText = "";
var errorDiv = document.getElementById("errorText");
try {
if(!(isNaN(lname.value)) || (lname.value === "")){
lname.style.background = "rgb(255,233,233)";
throw "Please enter your first name.";
} 
}
catch(message) {
validity = false;
messageText = message;
}
finally{
errorDiv.style.display = "block";
lnameComplete = validity;
errorDiv.innerHTML = messageText;
}
}
function verifyEmail() {
var validity = true;    
var messageText = "";
var errorDiv = document.getElementById("errorText");
try {
if(email === "") {
email.style.background = "rgb(255,233,233)";
throw "Please enter your email.";
}
}
catch(message) {
validity = false;
messageText = message;
}
finally{
numErrorDiv.style.display = "block";
emailComplete = validity;
errorDiv.innerHTML = messageText;
}
}
function validateForm(e) {
if (e.preventDefault) {
e.preventDefault(); //prevent form from submitting
} else {
e.returnValue = false; //prevent form from submitting in IE8
}
formValidity = true; //reset value for revalidation
verifyEmail();
verifyFname();
verifyLname();
if(formValidity === true) {
document.getElementsByTagName("form")[0].submit();
}
}
function createEventListeners() {
var form = document.getElementsByTagName("form")[0];
if (form.addEventListener){
form.addEventListener("submit", validateForm, false);
} else if(form.attachEvent) {
form.attachEvent("onsubmit", validateForm);
}
}
if (window.addEventListener) {
window.addEventListener("load", createEventListeners, false);
} else if(window.attachEvent) {
window.attachEvent("onload", createEventListeners);
}

Answer 1

看起来您试图访问一个不存在的字段。

在这里你已经得到字段的值

var fname = document.getElementById("firstname").value;
var lname = document.getElementById("lastname").value;
var email = document.getElementById("emailaddress").value;

在比较中，您尝试再次访问值字段。但你已经有了普通价值的

if(!(isNaN(lname.value)) || (lname.value === "")){
}

用这种方式代替

if(!(isNaN(lname)) || (lname === "")){
}