The definition and detailed analysis of bubbling events

The definition and usage of bubbling events

Bubbling events mean that in web development, when an element triggers an event, the event will Propagates from top to bottom along the DOM tree. This propagation method is similar to the bubbling process, so it is called "bubble event". During the bubbling process, the event is first triggered on the topmost element and then propagates down to the bottommost element.

Bubbling events are widely used and can be used to implement many functions, such as form validation, menu hiding, dynamic loading of elements, etc. The following will take form verification as an example to introduce the specific use of bubbling events.

First, we create a simple HTML form and add some input boxes and a submit button. The code is as follows:

<form id="myForm">
  <input type="text" id="name" placeholder="请输入姓名">
  <input type="email" id="email" placeholder="请输入邮箱">
  <input type="password" id="password" placeholder="请输入密码">
  <button type="submit">提交</button>
</form>

Next, we need to add an event listener to the form element for verification when the user submits the form. We will use JavaScript code to implement this functionality. The code is as follows:

// 获取表单元素
const myForm = document.getElementById('myForm');

// 添加事件监听器
myForm.addEventListener('submit', function (event) {
  event.preventDefault(); // 阻止表单提交的默认行为

  // 获取各个输入框的值
  const nameValue = document.getElementById('name').value;
  const emailValue = document.getElementById('email').value;
  const passwordValue = document.getElementById('password').value;

  // 进行表单验证
  if (nameValue === '') {
    alert('请输入姓名');
    return;
  }

  if (emailValue === '') {
    alert('请输入邮箱');
    return;
  }

  if (passwordValue === '') {
    alert('请输入密码');
    return;
  }

  // 表单验证通过，可以进行提交操作
  alert('表单提交成功！');
});

The above code implements a simple form validation function. When the user clicks the submit button, the submit event is triggered and propagates downward from the top-most form element. In the event listener, we first call the event.preventDefault() method to prevent the form's default submission behavior. Then, we obtain the value of each input box through JavaScript and perform simple verification. If there are unfilled items in the form, a prompt box will pop up and event propagation will be terminated. If all form items pass verification, a prompt box indicating successful submission will pop up.

As can be seen from the above code, bubbling events can not only be used to provide user-friendly prompts, but can also control the form submission behavior and perform other operations. By flexibly utilizing bubbling events, we can achieve more powerful functions.

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