简单的图像滑块不起作用（jQuery）

Question

我正在使用jQuery创建一个简单的滑块。

问题：滑块消失和/或塌陷（刷新后消失之前可以看到它）。

我正在尝试做的事情：使图像的位置absolute ，然后使用JavaScript通过脚本中的display属性显示第nth索引。

不知道是CSS还是JavaScript使其隐藏。 有什么想法我做错了吗？

 $(document).ready(function() { $('#sidebar-btn').click(function() { $('#sidebar-nav').toggleClass('visible'); }); }); var index = 0; function plusIndex(n) { index = index + 1; showImage(index); } /* SLIDER */ showImage(1); /* Slider function */ function showImage(n) { var i; var x = document.getElementsByClassName("slider-img"); // for next slide - forward. if(n > x.length) { index = 1 }; // for prev slide - backwards if(n < 1 ) { index = x.length /* last one */ }; for(i=0; i<x.length; i++) { x[i].style.display = "none"; } x[index-1].style.display = "block"; } 

 .updates-box { background-color: #f5f5f5; text-align: center; padding: 2rem; } .updates-item-headline { font-weight: bold; } .updates-item { padding: 1rem; margin: 1rem auto; } .slider { position: relative; } .slider-img { position: absolute; } .slider .slider-btn { position: absolute; color: black; width: 50px; border:none; border-radius: 25px; top: 190px; font-size: 35px; margin: 1rem; } .slider #slide-btn2 { position: relative; float: right; } .slider #slide-btn1:hover { box-shadow: 10px 0px 20px 0px black; } .slider #slide-btn2:hover { box-shadow: 10px 0px 20px 0px black; } 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <div class="hero-box"> <div id="slide-wrapper"> <div class="slider"> <div class="slide"> <picture> <source media="(max-width: 620px)" srcset="img/hero-slider-mobile.jpg"> <source media="(min-width: 621)" srcset="img/hero-slider-tablet.jpg"> <img class="slider-img" src="img/hero-slider-home.jpg" alt="Flowers"> </picture> </div> <div class="slide"> <picture> <source media="(max-width: 620px)" srcset="img/slide-2-mobile.jpg"> <source media="(min-width: 621)" srcset="img/slide-2-tablet.jpg"> <img class="slider-img" src="img/slide-2-home.jpg" alt="Flowers"> </picture> </div> <button class="slider-btn" id="slide-btn1">&#10094;</button> <button class="slider-btn" id="slide-btn2">&#10095;</button> </div> </div> </div> <div class="updates-box"> <div class="updates-item-headline"> <p> UPCOMING EVENT DATES</p> </div> <div class="updates-item"> <img class="update-icon" src="img/dates-icon.png"> <p><b>Thursday 3 August</b></p> <p> Open Seminar Enrollment</p> </div> <div class="updates-item"> <img class="update-icon" src="img/dates-icon.png"> <p><b>Thursday 3 August</b></p> <p> Open Seminar Enrollment</p> </div> <div class="updates-item-4"> <img class="update-icon" src="img/dates-icon.png"> <p><b>Thursday 3 August</b></p> <p> Open Seminar Enrollment</p> </div> </div> 

Answer 1

在您的代码段中...您有错误：

无法读取未定义的属性“样式”

该错误表明x[index-1]未定义。
它是未定义的，因为在上述if条件中的两个条件之一中定义了index ...两者都评估为false 。

1. 在if(n > x.length) ：n = 1且x.length = 2
2. if(n < 1 ) ：n = 1

因此index是“未定义的”。

然后是for循环，将所有图像设置为display:none 。
这就是为什么您可能会在刷新后看到它们几毫秒的原因。

最后， x[index-1]也是未定义的。因此，没有图像设置回display:block 。

我建议您添加一个条件可以评估为true ：

if(n >= 1 && n<=x.length ){ index = n; };

 console.clear(); $(document).ready(function() { $('#sidebar-btn').click(function() { $('#sidebar-nav').toggleClass('visible'); }); }); var index = 0; function plusIndex(n) { index = index + 1; showImage(index); } /* SLIDER */ showImage(1); /* Slider function */ function showImage(n) { var i; var x = document.getElementsByClassName("slider-img"); // for next slide - forward. if(n > x.length) { index = 1 }; // for prev slide - backwards if(n < 1 ) { index = x.length /* last one */ }; if(n >= 1 && n<=x.length ){ index = n; }; // ADD THIS CASE for(i=0; i<x.length; i++) { x[i].style.display = "none"; } x[index-1].style.display = "block"; } 

 .updates-box { background-color: #f5f5f5; text-align: center; padding: 2rem; } .updates-item-headline { font-weight: bold; } .updates-item { padding: 1rem; margin: 1rem auto; } .slider { position: relative; } .slider-img { position: absolute; } .slider .slider-btn { position: absolute; color: black; width: 50px; border:none; border-radius: 25px; top: 190px; font-size: 35px; margin: 1rem; } .slider #slide-btn2 { position: relative; float: right; } .slider #slide-btn1:hover { box-shadow: 10px 0px 20px 0px black; } .slider #slide-btn2:hover { box-shadow: 10px 0px 20px 0px black; } 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <div class="hero-box"> <div id="slide-wrapper"> <div class="slider"> <div class="slide"> <picture> <source media="(max-width: 620px)" srcset="img/hero-slider-mobile.jpg"> <source media="(min-width: 621)" srcset="img/hero-slider-tablet.jpg"> <img class="slider-img" src="http://lorempixel.com/400/200/cats" alt="Flowers"> </picture> </div> <div class="slide"> <picture> <source media="(max-width: 620px)" srcset="img/slide-2-mobile.jpg"> <source media="(min-width: 621)" srcset="img/slide-2-tablet.jpg"> <img class="slider-img" src="http://lorempixel.com/400/200/nature" alt="Flowers"> </picture> </div> <button class="slider-btn" id="slide-btn1">&#10094;</button> <button class="slider-btn" id="slide-btn2">&#10095;</button> </div> </div> </div> <div class="updates-box"> <div class="updates-item-headline"> <p> UPCOMING EVENT DATES</p> </div> <div class="updates-item"> <img class="update-icon" src="img/dates-icon.png"> <p><b>Thursday 3 August</b></p> <p> Open Seminar Enrollment</p> </div> <div class="updates-item"> <img class="update-icon" src="img/dates-icon.png"> <p><b>Thursday 3 August</b></p> <p> Open Seminar Enrollment</p> </div> <div class="updates-item-4"> <img class="update-icon" src="img/dates-icon.png"> <p><b>Thursday 3 August</b></p> <p> Open Seminar Enrollment</p> </div> </div>