Master bubbling event handling methods: Solve problems caused by JS bubbling events

Solving the problems caused by JS bubbling events: To understand how to handle bubbling events at once, you need specific code examples

When writing JavaScript code, we often Will involve event handling. An important concept in event processing is bubbling events. A bubbling event means that when an event on an element is triggered, its parent elements will also trigger the same event in turn. While this mechanism can be very useful in some situations, it can sometimes cause problems. This article will introduce how to handle bubbling events and provide specific code examples.

1. Problems with bubbling events
Before understanding bubbling events, let us first take a look at the problems that may be caused by bubbling events. Suppose we have an HTML structure as follows:

<div class="outer">
  <div class="inner">
    <button class="btn">点击</button>
  </div>
</div>

Then, we use JavaScript to add a click event handler for the button:

var btn = document.querySelector('.btn');
btn.addEventListener('click', function() {
  console.log('按钮被点击了');
});

Now, when we click the button, we will see the console "The button was clicked" is output. This is normal because we added a click event handler to the button.

However, suppose we also add a click event handler to the outer div:

var outer = document.querySelector('.outer');
outer.addEventListener('click', function() {
  console.log('外层div被点击了');
});

Then, when we click the button, not only will "The button was clicked" be output, but also Output "The outer div was clicked". This is the problem caused by bubbling events: when a button is clicked, the click event is also triggered on its parent element.

2. How to handle bubbling events
In order to solve the problems caused by bubbling events, we can use the following processing methods:

1. Stop bubbling: pass Call the stopPropagation method of the event object to stop the bubbling of the event. The sample code is as follows:

var btn = document.querySelector('.btn');
btn.addEventListener('click', function(event) {
  event.stopPropagation(); // 停止冒泡
  console.log('按钮被点击了');
});

2. Prevent default behavior: Some elements will perform certain behaviors by default. For example, clicking on the a tag will jump to the specified link. You can prevent an element's default behavior by calling the event object's preventDefault method. The sample code is as follows:

var link = document.querySelector('a');
link.addEventListener('click', function(event) {
  event.preventDefault(); // 阻止默认行为
  console.log('链接被点击了');
});

3. Use event delegation: Event delegation refers to binding the event handler to the parent element and processing events on the child elements through the event bubbling mechanism. This method can reduce memory usage and improve performance. The sample code is as follows:

var outer = document.querySelector('.outer');
outer.addEventListener('click', function(event) {
  if (event.target.classList.contains('btn')) { // 判断事件的目标元素是否是按钮
    console.log('按钮被点击了');
  }
});

Through event delegation, you only need to bind an event handler to the parent element to handle events of multiple child elements, which greatly simplifies the code.

Summary:
When using JavaScript to write event processing code, we need to pay attention to the problems caused by bubbling events. By stopping bubbling, preventing default behavior, and using event delegation, we can effectively solve the problems caused by bubbling events. At the same time, this article also provides specific code examples, hoping to help readers better understand and apply the bubbling event processing method.

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