我的背景颜色没有使用javascript更改

时间：2018-07-15 21:16:01

标签： javascript jquery html css

我将不胜感激，我想我将完全错误地编写此代码。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BLUE> click> GREEN。它永远不会经历三种颜色。是否有其他方式编写if语句？还是其他我不知道的方法会让我有条件地更改CSS样式？

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>

4 个答案:

答案 0 :(得分：2)

这是正确的Javascript：

当我们收听被单击的myBtn时，我们只需要一个实例，因此我将您的所有实例都移到了一个实例中。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在本文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>

答案 1 :(得分：2)

您甚至不需要jquery。因此，请使用纯JavaScript。我还建议使用ES6（在const上使用let和var等）。

与其在事件处理程序声明周围添加if语句，不如在事件处理程序声明中添加它们（请参阅const color）。

还要注意，background样式不仅具有颜色（例如重复），还具有更多的值。您可以只设置并检查backgroundColor，也可以按空格分隔background值，然后输入第一个条目（这是实际的颜色集）。

const header = document.getElementById('header')

document.getElementById("myBtn").addEventListener("click", () => {
  const headerBg = header.style.background.split(" ")[0]
  const color = headerBg == "red" ? "green" : headerBg == "darkblue" ? "red" : "darkblue"
  changeBg(header, color)
})

const changeBg = (n, color) => {
  n.style.background = color
}
<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
</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>
</body>

</html>

答案 2 :(得分：1)

代码中的问题是，您不断向元素添加越来越多的事件处理程序，而不是使用一个事件处理程序来调整其行为。

由于您已经包含了jquery，我希望您会接受使用它的答案。您可以使用此代码替换main.js，它应该会为您提供所需的结果。

$(document).on('click', '#myBtn', function() {
    let color;
    switch (document.getElementById('header').style.background) {
        case 'darkblue':
            color = 'red';
            break;
        case 'red':
            color = 'green';
            break;
        default:
            color = 'darkblue';
            break;
    }
    $('#header').css('background', color);
});

jQuery文档单击处理程序是我发现自己经常使用的一种模式。它绑定到文档，因此您不必担心在创建元素后运行代码。如果该元素存在，即使它在某个时候被删除，单击该处理程序也会触发。

您会注意到document.getElementById('header').style.background仍然是常规javascript，这是因为使用$('#header').css('background')会为您提供一个与颜色名称字符串不匹配的RGB计算值。

答案 3 :(得分：1)

像这样的事情怎么样，只是具有一系列颜色，然后单击增加索引，并使用mod运算符获取正确的索引。

  $(document).ready(function() {
  let i = 0;
  let colors = ['red', 'green', 'blue','purple', 'orange', 'pink'];
  $('button').click(function() {
    $('.header').css("background-color", colors[i++ % colors.length]);
  })
});

https://jsfiddle.net/s0L4mgea/

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