Javascript $('li').length 调用抛出未捕获的异常
Javascript $('li').length call throws uncaught exception
我构建了一个带有旋转木马图像滑块的小网页。滑块具有按钮，单击这些按钮会触发图像更改，并且还会在滑块下方显示一些相应的文本。现在滑块有四个图像。当我点击第四张图片后的 'next image' 按钮时，幻灯片和相应的文本简介应该重新开始，但我的 Javascript 或 JSON 却抛出了错误。如果我在页面首次加载时单击 'previous image' 按钮，则会抛出相同的错误。这让我相信问题出在增量减量函数附近，但当然我可能是错的。错误如下，我提前为其奇怪的代码块格式道歉。我对 js 异常没有经验，所以我不确定发布它们的最佳格式是什么。我将所有 html、css 和 js 都放在一个代码块中，因为我不确定是 html 还是 js 导致抛出异常。任何见解将不胜感激！
Uncaught TypeError: Cannot read property 'Imagedes' of undefinedmoveRight @ ShowcaseWebsiteTest.html:272(anonymous function) @ ShowcaseWebsiteTest.html:281m.event.dispatch @ jquery-latest.min.js:3m.event.add.r.handle @ jquery-latest.min.js:3
<html>
<title>Showcase Website</title>
<meta charset="UTF-8">
<head>
<style>
header {
width:100%;
background-color:lightblue;
text-align:center;
padding:5px;
}
/*Use of the child selector Combinator*/
header > h1 {
color: black;
}
/*Use of Pseudo-Class*/
p::first-letter {
font-size: x-large;
}
/*Use of the Navigation Bar*/
nav {
line-height:30px;
background-color:#8f8f8f;
height:1500px;
width:100px;
float:left;
padding:5px;
position: relative;
}
/*Pseudo-Class*/
a:visited {
color: #00BDA0;
}
/*Using Box Model, Border, Outline, Margin, Padding, Dimension, Float*/
section {
height:350px;
width:100%;
padding:10px 0 30px 2px;
border: 3px solid gray;
margin: 0px 1px 5px 25px;
}
/*Using the "display: none" property to hide a previous title*/
h1.hidden{
display: none;
}
/*Using Positioning*/
article.art1 {
height:350px;
width:350px;
float:center;
padding-top:100px;
padding-left:50px;
position: relative;
top: 125px;
left: 85px;
}
/*Using Positioning*/
aside {
height:350px;
width:350px;
float:right;
padding-top:10px;
padding-right:150px;
position: relative;
top: 45px;
left: 45px;
right: 50px;
}
footer {
background-color:lightblue;
color:white;
clear:both;
text-align:center;
padding:5px;
}
@import url(http://fonts.googleapis.com/css?family=Open+Sans:400,300,600);
html {
border-top: 5px solid #fff;
background: #58DDAF;
color: #2a2a2a;
}
html, body {
margin: 0;
padding: 0;
font-family: 'Open Sans';
}
h1 {
color: #fff;
text-align: center;
font-weight: 300;
}
#slider {
position: relative;
overflow: hidden;
margin: 20px auto 0 auto;
border-radius: 4px;
}
#slider ul {
position: relative;
margin: 0;
padding: 0;
height: 200px;
list-style: none;
}
#slider ul li {
position: relative;
display: block;
float: left;
margin: 0;
padding: 0;
width: 500px;
height: 300px;
background: #ccc;
text-align: center;
line-height: 300px;
}
button.control_prev, button.control_next {
position: absolute;
top: 40%;
z-index: 999;
display: block;
padding: 2% 2%;
width: auto;
height: auto;
background: #2a2a2a;
color: #fff;
text-decoration: none;
font-weight: 600;
font-size: 10px;
opacity: 0.8;
cursor: pointer;
border:solid transparent;
}
button.control_prev:hover, button.control_next:hover {
opacity: 1;
-webkit-transition: all 0.2s ease;
}
button.control_prev {
border-radius: 0 2px 2px 0;
}
button.control_next {
right: 0;
border-radius: 2px 0 0 2px;
}
.slider_option {
position: relative;
margin: 10px auto;
width: 160px;
font-size: 18px;
}
.active{
color:red;
}
.imageDes{
color:red;
}
</style>
</head>
<body>
<main>
<header>
<h1>Text</h1>
</header>
<nav>
<a href="">Home</a>
<br><a href="">How To</a>
<br><a href="">Additional</a>
<br>
</nav>
<section class="section3">
<h1>Text</h1>
<p>
Text
</p>
<ul>
<li>Text</li>
<li>Text</li>
<li>Text</li>
</ul>
</section>
<div id="slider">
<button class="control_next">></button>
<button class="control_prev"><</button>
<ul>
<li class="active" data-des="Image 1">SLIDE 1</li>
<li data-des="Image 2" style="background: #aaa;">SLIDE 2</li>
<li data-des="Image 3">SLIDE 3</li>
<li data-des="Image 4" style="background: #aaa;">SLIDE 4</li>
</ul>
</div>
<div class="imageDes"></div>
<footer>
Name Here
</footer>
</main>
<script src="http://code.jquery.com/jquery-latest.min.js" type="text/javascript"></script>
<script>
var dataJson=[{"Imagedes":"Description for Image one which can be so long that it might extend upto 2 lines in most of the cases and that has to be rendered on image change"},
{"Imagedes":"Description for Image two which can be so long that it might extend upto 2 lines in most of the cases and that has to be rendered on image change"},
{"Imagedes":"Description for Image three which can be so long that it might extend upto 2 lines in most of the cases and that has to be rendered on image change"},
{"Imagedes":"Description for Image four which can be so long that it might extend upto 2 lines in most of the cases and that has to be rendered on image change"}]
var index=0;
$('.imageDes').text(dataJson[0].Imagedes);
jQuery(document).ready(function ($) {
$('#checkbox').change(function(){
setInterval(function () {
moveRight();
}, 3000);
});
var slideCount = $('#slider ul li').length;
var slideWidth = $('#slider ul li').width();
var slideHeight = $('#slider ul li').height();
var sliderUlWidth = slideCount * slideWidth;
$('#slider').css({ width: slideWidth, height: slideHeight });
$('#slider ul').css({ width: sliderUlWidth, marginLeft: - slideWidth });
$('#slider ul li:last-child').prependTo('#slider ul');
function moveLeft() {
$('#slider ul').animate({
left: + slideWidth
}, 200, function () {
$('#slider ul li:last-child').prependTo('#slider ul');
$('#slider ul').css('left', '');
});
if(index<=0)
index=$('li').length-1;
else
index--
$('.imageDes').text(dataJson[index].Imagedes);
};
function moveRight() {
$('#slider ul').animate({
left: - slideWidth
}, 200, function () {
$('#slider ul li:first-child').appendTo('#slider ul');
$('#slider ul').css('left', '');
});
if(index+1>=$('li').length)
index=0;
else
index++
$('.imageDes').text(dataJson[index].Imagedes);
};
$('button.control_prev').click(function () {
moveLeft();
});
$('button.control_next').click(function () {
moveRight();
});
});
</script>
</body>
</html>
在 moveRight() 和 moveLeft() 函数中更改 $('li').length 以使用 slideCount 变量。
现在 $('li').length return 是页面上 li 元素的总数（大于轮播幻灯片的数量）。这会导致您的 index 变量被设置为超出您的 dataJson 数组的值，因此导致 dataJson[index] 到 return undefined。
我构建了一个带有旋转木马图像滑块的小网页。滑块具有按钮，单击这些按钮会触发图像更改，并且还会在滑块下方显示一些相应的文本。现在滑块有四个图像。当我点击第四张图片后的 'next image' 按钮时，幻灯片和相应的文本简介应该重新开始，但我的 Javascript 或 JSON 却抛出了错误。如果我在页面首次加载时单击 'previous image' 按钮，则会抛出相同的错误。这让我相信问题出在增量减量函数附近，但当然我可能是错的。错误如下，我提前为其奇怪的代码块格式道歉。我对 js 异常没有经验，所以我不确定发布它们的最佳格式是什么。我将所有 html、css 和 js 都放在一个代码块中，因为我不确定是 html 还是 js 导致抛出异常。任何见解将不胜感激！
Uncaught TypeError: Cannot read property 'Imagedes' of undefinedmoveRight @ ShowcaseWebsiteTest.html:272(anonymous function) @ ShowcaseWebsiteTest.html:281m.event.dispatch @ jquery-latest.min.js:3m.event.add.r.handle @ jquery-latest.min.js:3
<html>
<title>Showcase Website</title>
<meta charset="UTF-8">
<head>
<style>
header {
width:100%;
background-color:lightblue;
text-align:center;
padding:5px;
}
/*Use of the child selector Combinator*/
header > h1 {
color: black;
}
/*Use of Pseudo-Class*/
p::first-letter {
font-size: x-large;
}
/*Use of the Navigation Bar*/
nav {
line-height:30px;
background-color:#8f8f8f;
height:1500px;
width:100px;
float:left;
padding:5px;
position: relative;
}
/*Pseudo-Class*/
a:visited {
color: #00BDA0;
}
/*Using Box Model, Border, Outline, Margin, Padding, Dimension, Float*/
section {
height:350px;
width:100%;
padding:10px 0 30px 2px;
border: 3px solid gray;
margin: 0px 1px 5px 25px;
}
/*Using the "display: none" property to hide a previous title*/
h1.hidden{
display: none;
}
/*Using Positioning*/
article.art1 {
height:350px;
width:350px;
float:center;
padding-top:100px;
padding-left:50px;
position: relative;
top: 125px;
left: 85px;
}
/*Using Positioning*/
aside {
height:350px;
width:350px;
float:right;
padding-top:10px;
padding-right:150px;
position: relative;
top: 45px;
left: 45px;
right: 50px;
}
footer {
background-color:lightblue;
color:white;
clear:both;
text-align:center;
padding:5px;
}
@import url(http://fonts.googleapis.com/css?family=Open+Sans:400,300,600);
html {
border-top: 5px solid #fff;
background: #58DDAF;
color: #2a2a2a;
}
html, body {
margin: 0;
padding: 0;
font-family: 'Open Sans';
}
h1 {
color: #fff;
text-align: center;
font-weight: 300;
}
#slider {
position: relative;
overflow: hidden;
margin: 20px auto 0 auto;
border-radius: 4px;
}
#slider ul {
position: relative;
margin: 0;
padding: 0;
height: 200px;
list-style: none;
}
#slider ul li {
position: relative;
display: block;
float: left;
margin: 0;
padding: 0;
width: 500px;
height: 300px;
background: #ccc;
text-align: center;
line-height: 300px;
}
button.control_prev, button.control_next {
position: absolute;
top: 40%;
z-index: 999;
display: block;
padding: 2% 2%;
width: auto;
height: auto;
background: #2a2a2a;
color: #fff;
text-decoration: none;
font-weight: 600;
font-size: 10px;
opacity: 0.8;
cursor: pointer;
border:solid transparent;
}
button.control_prev:hover, button.control_next:hover {
opacity: 1;
-webkit-transition: all 0.2s ease;
}
button.control_prev {
border-radius: 0 2px 2px 0;
}
button.control_next {
right: 0;
border-radius: 2px 0 0 2px;
}
.slider_option {
position: relative;
margin: 10px auto;
width: 160px;
font-size: 18px;
}
.active{
color:red;
}
.imageDes{
color:red;
}
</style>
</head>
<body>
<main>
<header>
<h1>Text</h1>
</header>
<nav>
<a href="">Home</a>
<br><a href="">How To</a>
<br><a href="">Additional</a>
<br>
</nav>
<section class="section3">
<h1>Text</h1>
<p>
Text
</p>
<ul>
<li>Text</li>
<li>Text</li>
<li>Text</li>
</ul>
</section>
<div id="slider">
<button class="control_next">></button>
<button class="control_prev"><</button>
<ul>
<li class="active" data-des="Image 1">SLIDE 1</li>
<li data-des="Image 2" style="background: #aaa;">SLIDE 2</li>
<li data-des="Image 3">SLIDE 3</li>
<li data-des="Image 4" style="background: #aaa;">SLIDE 4</li>
</ul>
</div>
<div class="imageDes"></div>
<footer>
Name Here
</footer>
</main>
<script src="http://code.jquery.com/jquery-latest.min.js" type="text/javascript"></script>
<script>
var dataJson=[{"Imagedes":"Description for Image one which can be so long that it might extend upto 2 lines in most of the cases and that has to be rendered on image change"},
{"Imagedes":"Description for Image two which can be so long that it might extend upto 2 lines in most of the cases and that has to be rendered on image change"},
{"Imagedes":"Description for Image three which can be so long that it might extend upto 2 lines in most of the cases and that has to be rendered on image change"},
{"Imagedes":"Description for Image four which can be so long that it might extend upto 2 lines in most of the cases and that has to be rendered on image change"}]
var index=0;
$('.imageDes').text(dataJson[0].Imagedes);
jQuery(document).ready(function ($) {
$('#checkbox').change(function(){
setInterval(function () {
moveRight();
}, 3000);
});
var slideCount = $('#slider ul li').length;
var slideWidth = $('#slider ul li').width();
var slideHeight = $('#slider ul li').height();
var sliderUlWidth = slideCount * slideWidth;
$('#slider').css({ width: slideWidth, height: slideHeight });
$('#slider ul').css({ width: sliderUlWidth, marginLeft: - slideWidth });
$('#slider ul li:last-child').prependTo('#slider ul');
function moveLeft() {
$('#slider ul').animate({
left: + slideWidth
}, 200, function () {
$('#slider ul li:last-child').prependTo('#slider ul');
$('#slider ul').css('left', '');
});
if(index<=0)
index=$('li').length-1;
else
index--
$('.imageDes').text(dataJson[index].Imagedes);
};
function moveRight() {
$('#slider ul').animate({
left: - slideWidth
}, 200, function () {
$('#slider ul li:first-child').appendTo('#slider ul');
$('#slider ul').css('left', '');
});
if(index+1>=$('li').length)
index=0;
else
index++
$('.imageDes').text(dataJson[index].Imagedes);
};
$('button.control_prev').click(function () {
moveLeft();
});
$('button.control_next').click(function () {
moveRight();
});
});
</script>
</body>
</html>
在 moveRight() 和 moveLeft() 函数中更改 $('li').length 以使用 slideCount 变量。
现在 $('li').length return 是页面上 li 元素的总数（大于轮播幻灯片的数量）。这会导致您的 index 变量被设置为超出您的 dataJson 数组的值，因此导致 dataJson[index] 到 return undefined。