为什么我的引导下拉按钮不起作用？答案

【问题标题】：Why is my bootstrap dropdown button not working?为什么我的引导下拉按钮不起作用？
【发布时间】：2020-12-11 13:06:55
【问题描述】：

当在下拉菜单中选择一个选项时，即使按下它，它也不会在按钮上改变。我也尝试在 javascript 上进行控制台记录，但它不打印，而是在 chrome 检查器上显示以下错误：

index.js:26 Uncaught TypeError: Cannot read property 'value' of null
    at getSelectValue (index.js:26)
    at index.js:29

我的html是：

<!DOCTYPE html>
<html lang="en" dir="ltr">

<head>
  <meta charset="utf-8">
  <title>Titlee</title>

  <!-- Favicon -->
  <link rel="short icon" type="image" href="dicelogo.png">

  <!-- Bootstrap, CSS -->
  <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.5.0/css/bootstrap.min.css" integrity="sha384-9aIt2nRpC12Uk9gS9baDl411NQApFmC26EwAOH8WgZl5MYYxFfc+NcPb1dKGj7Sk" crossorigin="anonymous">
  <link rel="stylesheet" href="styles.css">

  <!-- Google Font -->
  <link href="https://fonts.googleapis.com/css2?family=PT+Mono&display=swap" rel="stylesheet">
  <link href="https://fonts.googleapis.com/css?family=Indie+Flower|Lobster" rel="stylesheet">

  <!-- Jquery Links -->
  <script src="https://code.jquery.com/jquery-3.3.1.slim.min.js" integrity="sha384-q8i/X+965DzO0rT7abK41JStQIAqVgRVzpbzo5smXKp4YfRvH+8abtTE1Pi6jizo" crossorigin="anonymous"></script>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper.min.js" integrity="sha384-UO2eT0CpHqdSJQ6hJty5KVphtPhzWj9WO1clHTMGa3JDZwrnQq4sF86dIHNDz0W1" crossorigin="anonymous"></script>
  <script src="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js" integrity="sha384-JjSmVgyd0p3pXB1rRibZUAYoIIy6OrQ6VrjIEaFf/nJGzIxFDsf4x0xIM+B07jRM" crossorigin="anonymous"></script>
</head>

<body>
  
  <div class="container-fluid user-interaction">
    <h1>How to play?</h1>
    <h5>Write down your choices here (you can choose up to 4):</h5>


    <!-- Dropdown Button -->
    <div class="dropdown">
      <button class="btn btn-info dropdown-toggle" type="button" id="dropdownMenu1" data-toggle="dropdown" aria-haspopup="true" aria-expanded="true">
        2
        <span class="caret"></span>
      </button>
      <ul id="list" class="dropdown-menu dropdown-info" onchange="getSelectedValue();" aria-labelledby="dropdownMenu1">
        <li><a href="#">2</a></li>
        <li><a href="#">3</a></li>
        <li><a href="#">4</a></li>
      </ul>
    </div>
    <input type="text" name="" value="" placeholder="">
  </div>


  <script src="index.js" charset="utf-8">
  </script>
</body>

<footer>
  ???? Thanks for playing ????
</footer>



</html>

我的 javascript 是：

// Default Dice
// 1st image
var randomNumber1 = Math.floor(Math.random() * 6 + 1);
var Image1 = "dice" + randomNumber1 + ".png";
document.querySelectorAll("img")[1].setAttribute("src", Image1);

// 2nd image
var randomNumber2 = Math.floor(Math.random() * 6 + 1);
var Image2 = "dice" + randomNumber2 + ".png";
document.querySelectorAll("img")[2].setAttribute("src", Image2);

// 3rd image
var randomNumber3 = Math.floor(Math.random() * 6 + 1);
var Image3 = "dice" + randomNumber3 + ".png";
document.querySelectorAll("img")[3].setAttribute("src", Image3);

// 4th image
var randomNumber3 = Math.floor(Math.random() * 6 + 1);
var Image4 = "dice" + randomNumber3 + ".png";
document.querySelectorAll("img")[4].setAttribute("src", Image4);

var diceNumbers = []

// selectedNumber
function getSelectValue() {
  var selectedValue = document.getElementById("list").value;
  console.log(selectedValue);
}
getSelectValue();


// Determining Winner

如何使选择的数字被选中并打印在控制台日志上？提前致谢

【问题讨论】：

var selectedValue = document.getElementById("list") 您没有具有此 ID 的项目
@Unbywyd 即使在我将 Id 添加到
另见stackoverflow.com/questions/22383547/…

标签： javascript html bootstrap-4

【解决方案1】：

Bootstrap 的下拉菜单看起来与 html select 相似，但行为不同。您需要编写脚本来处理每个li 元素上的click 事件。

我想你会想要这样的东西：

let links = document.querySelectorAll('#list li')
links.forEach((el) => {
  el.addEventListener('click', (event) => {
    let val = event.target.innerText
    document.getElementById('dropdownMenu1').innerHTML = `${val}<span class="caret"></span>`
    console.log(val)
  })
})

<!-- Bootstrap, CSS -->
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.5.0/css/bootstrap.min.css" integrity="sha384-9aIt2nRpC12Uk9gS9baDl411NQApFmC26EwAOH8WgZl5MYYxFfc+NcPb1dKGj7Sk" crossorigin="anonymous">
<link rel="stylesheet" href="styles.css">

<!-- Google Font -->
<link href="https://fonts.googleapis.com/css2?family=PT+Mono&display=swap" rel="stylesheet">
<link href="https://fonts.googleapis.com/css?family=Indie+Flower|Lobster" rel="stylesheet">

<!-- Jquery Links -->
<script src="https://code.jquery.com/jquery-3.3.1.slim.min.js" integrity="sha384-q8i/X+965DzO0rT7abK41JStQIAqVgRVzpbzo5smXKp4YfRvH+8abtTE1Pi6jizo" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper.min.js" integrity="sha384-UO2eT0CpHqdSJQ6hJty5KVphtPhzWj9WO1clHTMGa3JDZwrnQq4sF86dIHNDz0W1" crossorigin="anonymous"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js" integrity="sha384-JjSmVgyd0p3pXB1rRibZUAYoIIy6OrQ6VrjIEaFf/nJGzIxFDsf4x0xIM+B07jRM" crossorigin="anonymous"></script>
  
<!-- Dropdown Button -->
<div class="dropdown">
  <button class="btn btn-info dropdown-toggle" type="button" id="dropdownMenu1" data-toggle="dropdown" aria-haspopup="true" aria-expanded="true">
    2
    <span class="caret"></span>
  </button>
  <ul id="list" class="dropdown-menu dropdown-info" aria-labelledby="dropdownMenu1">
    <li><a href="#">2</a></li>
    <li><a href="#">3</a></li>
    <li><a href="#">4</a></li>
  </ul>
</div>

【讨论】：

谢谢你是个天才......但我不明白 omg......前 3 行是什么意思？：let links = document.querySelectorAll('#list li ') links.forEach((el) => { el.addEventListener('click', (event) => {
querySelector() 收集可点击元素（lis），forEach() 迭代它们，addEventListener() 绑定点击事件。查看 w3schools，它包含您需要的所有参考资料w3schools.com