JavaScript轮播/滑块错误

Question

I was working on a personal project of making a slider using pure javascript. 我当时正在从事一个使用纯JavaScript制作滑块的个人项目。 But The js code is not working. 但是js代码无法正常工作。 When I click the next button, the console shows an error that next() is not a function. 当我单击下一步按钮时，控制台显示错误消息next（）不是函数。 Same with the Previous button it says prev() is not defined. 与上一个按钮相同，它表示未定义prev（）。 I tried everything I could but I am not able to find the answer. 我已尽力而为，但找不到答案。 It is confusing that I have declared both the functions but on click, I receive an error that functions are not functions. 我已经声明了两个函数，但是单击时会收到一个错误，即函数不是函数，这令人困惑。

main.js:38 Uncaught TypeError: next is not a function at HTMLElement. main.js：38 Uncaught TypeError：next不是HTMLElement的函数。 (main.js:38) （main.js：38）

JS Code: JS代码：

var next = document.getElementById("next");
var prev = document.getElementById("prev");
var ulist = document.getElementsByTagName("ul").lastChild;
var ulist1 = document.getElementsByTagName("ul").firstChild;
var slides = document.querySelectorAll("li");

for(var i=0; i<3; i++){
slides[i].style.display = 'none';
}

slides[0].classList.add("active");

document.getElementsByClassName("active")[0].style.display = "block";

function next() {
    document.getElementsByClassName("active")[0].classList.add("oldActive");
    document.getElementsByClassName("active")[0].classList.remove("active");
    if(Object.is(document.getElementsByClassName("oldActive")[0]) , ulist){
        slides[0].classList.add("active");
    }
    else{
        document.getElementsByClassName("oldActive")[0].nextElementSibling.classList.add("active");
    }
}

function prev() {
    document.getElementsByClassName("active")[0].classList.add("oldActive");
    document.getElementsByClassName("active")[0].classList.remove("active");
    if(Object.is(document.getElementsByClassName("oldActive")[0]) , ulist1){
        slides[2].classList.add("active");
    }
    else{
        document.getElementsByClassName("oldActive")[0].previousElementSibling.classList.add("active");
    }
}

next.addEventListener('click' , function() {
    next();
});


prev.addEventListener('click' , function() {
    prev();
});

HTML Code: HTML代码：

<!doctype html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Image/Content Slider with Pure JS</title>
    <link rel="stylesheet" href="css/style.css">
    <link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.0.13/css/all.css" integrity="sha384-DNOHZ68U8hZfKXOrtjWvjxusGo9WQnrNx2sqG0tfsghAvtVlRW3tvkXWZh58N9jp" crossorigin="anonymous">
</head>
<body>
    <header>
        <h1>A Responsive Image/Content Slider</h1>
        <p>It is made with HTML5, CSS3 and JavaScript</p>
    </header>
    <div class="left">
    <h1><i class="fas fa-arrow-left" id="prev"></i></h1>
    </div>
    <main>

        <div class="slider">
            <ul class="slides" id="slidelist">
                <li class="slide 1" name="slideo"><img src="images/hero_bg.jpeg" alt=""></li>
                <li class="slide 2" name="slideo"><img src="images/hero_bg1.jpeg" alt=""></li>
                <li class="slide 3" name="slideo"><img src="images/hero_bg1.jpeg" alt=""></li>
            </ul>               
        </div>

    </main>
    <div class="right">
    <h1><i class="fas fa-arrow-right"  id="next"></i></h1>
    </div>
    <script type="text/javascript" src="js/main.js"></script>
</body>
</html>

Answer 1

You have duplicate names of both next and prev - one as an element and later as function. 您具有next和prev的重复名称-一个作为元素，然后作为函数。 Rename one of the two to something else to avoid a naming conflict. 将两者之一重命名为其他名称，以避免命名冲突。

For instance: 例如：

var next = document.getElementById("next");
var prev = document.getElementById("prev");

to 至

var nextEl = document.getElementById("next");
var prevEl = document.getElementById("prev");

Answer 2

Working Fiddle : https://jsfiddle.net/o61pbg0z/ 工作小提琴： https : //jsfiddle.net/o61pbg0z/

What the issue was that the 问题是

var next = document.getElementById("next");
var prev = document.getElementById("prev");

And 和

function next() {
    document.getElementsByClassName("active")[0].classList.add("oldActive");
    document.getElementsByClassName("active")[0].classList.remove("active");
    if(Object.is(document.getElementsByClassName("oldActive")[0]) , ulist){
        slides[0].classList.add("active");
    }
    else{
        document.getElementsByClassName("oldActive")[0].nextElementSibling.classList.add("active");
    }
}

function prev() {
    document.getElementsByClassName("active")[0].classList.add("oldActive");
    document.getElementsByClassName("active")[0].classList.remove("active");
    if(Object.is(document.getElementsByClassName("oldActive")[0]) , ulist1){
        slides[2].classList.add("active");
    }
    else{
        document.getElementsByClassName("oldActive")[0].previousElementSibling.classList.add("active");
    }
}

Hence try giving both of them different names 因此，尝试给他们两个起不同的名字

Reason for failure : In JavaScript both function declaration and variable declarations are hoisted to the top of the function, if defined in a function, or the top of the global context, if outside a function. 失败原因：在JavaScript中，如果在函数中定义了函数声明和变量声明，则它们都被提升到函数的顶部；如果在函数外部，则被提升到全局上下文的顶部。 And function declaration takes precedence over variable declarations (but not over variable assignment). 并且函数声明优先于变量声明（但不优先于变量赋值）。

JavaScript轮播/滑块错误

问题描述

2 个解决方案

解决方案1
0 2018-06-03 17:59:43

解决方案2
0 已采纳 2018-06-03 18:06:37

JavaScript轮播/滑块错误

问题描述

2 个解决方案

解决方案1 0 2018-06-03 17:59:43

解决方案2 0 已采纳 2018-06-03 18:06:37

解决方案1
0 2018-06-03 17:59:43

解决方案2
0 已采纳 2018-06-03 18:06:37