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javascript - 我的背景颜色没有随 javascript 改变

问题描述

我将不胜感激，我想我要编写完全错误的代码。我想在单击按钮时更改标题颜色，使其变为蓝色>单击>红色>单击>绿色。到目前为止，我只能实现蓝色>单击>绿色。它从不经过三种颜色。是否有不同的方式来编写 if 语句？还是我不知道的另一种方法可以让我有一些有条件的css样式更改？

var mySwitch = document.getElementById('header').style.background;


if (mySwitch == "darkblue") {

    document.getElementById("myBtn").addEventListener("click", function(){
        document.getElementById("header").style.background = "red";

    });


}
else if (mySwitch == "red") {

    document.getElementById("myBtn").addEventListener("click", function(){
        document.getElementById("header").style.background = "green";

    });

}

else {
    document.getElementById("myBtn").addEventListener("click", function(){
        document.getElementById("header").style.background = "darkblue";

    });

} 
* {
    margin: 0;
    padding: 0;
list-style: none;
font-family: sans-serif;
}

#header {
    background: darkblue;
    color: white;
    
    display: flex;
    justify-content: space-around;
    height: 12vh;
}
#header h1 {
    text-align: left;
    margin-top: 30px;
}

.main-nav ul {
    padding: 0px;
    font-size: 1.5rem;
    display: flex;
    margin-top: 40px;
}

.main-nav a {
color: white;
padding: 20px;
text-decoration: none;

}
.main-nav a:hover {
color: rgb(255, 148, 148);
}

.hero-section {
background-image: url("https://stackoverflow.blog/wp-content/uploads/2018/01/BrutalLifeCycleJavascript.png");
background-position: center;
background-size: cover;
background-repeat: no-repeat;
height: 80vh;
color: white;
text-align: center;

display: flex;
flex-direction: column;
align-items: center;
justify-content: center;
}

button {
    background: black;
    height: 40px;
    width: 80px;
    color: white;
    margin-top: 20px;
    animation: jumpbutton 1s ease-out infinite;
    outline: none;
    border-radius: 15px;
}
<!DOCTYPE html>

<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<link rel="stylesheet" href="style.css" type="text/css">
<script src="https://code.jquery.com/jquery-3.2.1.slim.min.js" integrity="sha384-KJ3o2DKtIkvYIK3UENzmM7KCkRr/rE9/Qpg6aAZGJwFDMVNA/GpGFF93hXpG5KkN" crossorigin="anonymous"></script>
</head>
<body>

<header id="header">

    <nav class="main-nav">

<ul>
    <li><a href="#">Home</a></li>
    <li><a href="#">About</a></li>
    <li><a href="#">Contact</a></li>
</ul>
    </nav>

</header>

<div class="hero-section">

    <h1>JAVASCRIPT</h1>
<p id="paragraph">This is a testing environment</p>
<button type="submit"  id="myBtn"> CLICK ME </button>
</div>


<div class="about-box">
<p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Quam, asperiores!</p>

</div>

<!--  CHANGE HEADER COLOR, BACKGROUND & HERO IMAGE-->
















<!---                 -->
<script src="main.js"></script>
    
    <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.9/umd/popper.min.js" integrity="sha384-ApNbgh9B+Y1QKtv3Rn7W3mgPxhU9K/ScQsAP7hUibX39j7fakFPskvXusvfa0b4Q" crossorigin="anonymous"></script>
    <script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js" integrity="sha384-JZR6Spejh4U02d8jOt6vLEHfe/JQGiRRSQQxSfFWpi1MquVdAyjUar5+76PVCmYl" crossorigin="anonymous"></script>
</body>



</html>

标签： javascriptjqueryhtmlcss

解决方案

这是正确的 Javascript：

当我们听到 myBtn 被点击时，我们只需要一个实例，所以我移动了你的所有实例并将它们移到一个中。我还在 Javascript 中声明了颜色，因此您只需单击一次按钮即可激活颜色。

manniL 在这篇文章中给出了更高级的答案！

document.getElementById('header').style.background = "darkblue"; // Declare the initial background color here, so that you don't have to press "Click Me" twice to get it to work!

document.getElementById("myBtn").addEventListener("click", function(){

var mySwitch = document.getElementById('header').style.background;
  
if (mySwitch == "darkblue") { 

    document.getElementById("header").style.background = "red";

} else if (mySwitch == "red") {

  document.getElementById("header").style.background = "green";

} else {

  document.getElementById("header").style.background = "darkblue";

} 

});
* {
    margin: 0;
    padding: 0;
list-style: none;
font-family: sans-serif;
}

#header {
    background: darkblue;
    color: white;
    
    display: flex;
    justify-content: space-around;
    height: 12vh;
}
#header h1 {
    text-align: left;
    margin-top: 30px;
}

.main-nav ul {
    padding: 0px;
    font-size: 1.5rem;
    display: flex;
    margin-top: 40px;
}

.main-nav a {
color: white;
padding: 20px;
text-decoration: none;

}
.main-nav a:hover {
color: rgb(255, 148, 148);
}

.hero-section {
background-image: url("https://stackoverflow.blog/wp-content/uploads/2018/01/BrutalLifeCycleJavascript.png");
background-position: center;
background-size: cover;
background-repeat: no-repeat;
height: 80vh;
color: white;
text-align: center;

display: flex;
flex-direction: column;
align-items: center;
justify-content: center;
}

button {
    background: black;
    height: 40px;
    width: 80px;
    color: white;
    margin-top: 20px;
    animation: jumpbutton 1s ease-out infinite;
    outline: none;
    border-radius: 15px;
}
<!DOCTYPE html>

<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<link rel="stylesheet" href="style.css" type="text/css">
<script src="https://code.jquery.com/jquery-3.2.1.slim.min.js" integrity="sha384-KJ3o2DKtIkvYIK3UENzmM7KCkRr/rE9/Qpg6aAZGJwFDMVNA/GpGFF93hXpG5KkN" crossorigin="anonymous"></script>
</head>
<body>

<header id="header">

    <nav class="main-nav">

<ul>
    <li><a href="#">Home</a></li>
    <li><a href="#">About</a></li>
    <li><a href="#">Contact</a></li>
</ul>
    </nav>

</header>

<div class="hero-section">

    <h1>JAVASCRIPT</h1>
<p id="paragraph">This is a testing environment</p>
<button type="submit"  id="myBtn"> CLICK ME </button>
</div>


<div class="about-box">
<p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Quam, asperiores!</p>

</div>

<!--  CHANGE HEADER COLOR, BACKGROUND & HERO IMAGE-->
















<!---                 -->
<script src="main.js"></script>
    
    <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.9/umd/popper.min.js" integrity="sha384-ApNbgh9B+Y1QKtv3Rn7W3mgPxhU9K/ScQsAP7hUibX39j7fakFPskvXusvfa0b4Q" crossorigin="anonymous"></script>
    <script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js" integrity="sha384-JZR6Spejh4U02d8jOt6vLEHfe/JQGiRRSQQxSfFWpi1MquVdAyjUar5+76PVCmYl" crossorigin="anonymous"></script>
</body>



</html>

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