js 3个事件监听器 EventListeners

起因，目的:

我有2个显示器。某视频网站，我想一边播放视频，一边搞其他。但是，当我把鼠标移动到浏览器外面，点击一下别处，视频就会自动暂停. 这个叫做 事件监听！

blur, 在元素或窗口失去焦点时触发
focus, 与 blur 相反。
visibilitychange

1. 自己先写个播放视频的例子。

html + css + js , 一个文件

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Video Player Example</title>
    <style>
        
        body {
            font-family: Arial, sans-serif;
            background-color: #f4f4f4;
            text-align: center;
            padding: 10px;
        }

        video {
            width: 100%;
            max-width: 1800px;
            height: auto;
            margin-bottom: 3px;
        }

        p {
            color: #555;
        }
    </style>
</head>

<body>
    <h1>Video Player: a.mp4</h1>
    <video id="myVideo" controls>
        <source src="a.mp4" type="video/mp4">
        Your browser does not support the video tag.
    </video>

    <p id="status">The video is playing...</p>

    <script>
        const video = document.getElementById('myVideo');
        const status = document.getElementById('status');

        // 当窗口失去焦点时暂停视频
        window.addEventListener('blur', () => {
            video.pause();
            status.textContent = 'The video is paused because the window lost focus.';
        });

        // 当窗口重新获得焦点时恢复播放
        window.addEventListener('focus', () => {
            video.play();
            status.textContent = 'The video is playing...';
        });

        // 当页面变为不可见时暂停视频
        document.addEventListener('visibilitychange', () => {
            if (document.hidden) {
                video.pause();
                status.textContent = 'The video is paused because the page is not visible.';
            } else {
                video.play();
                status.textContent = 'The video is playing...';
            }
        });
    </script>

</body>
</html>

播放效果:
在这里插入图片描述

2. 浏览器中，执行下面这段 js 代码，会移除这3个事件监听函数。

// 获取窗口的 blur 和 focus 事件监听器
const blurListeners = getEventListeners(window).blur;
const focusListeners = getEventListeners(window).focus;

// 获取文档的 visibilitychange 事件监听器
const visibilityListeners = getEventListeners(document).visibilitychange;

// 移除 blur 事件监听器
blurListeners.forEach(listener => {
    window.removeEventListener('blur', listener.listener);
});

// 移除 focus 事件监听器
focusListeners.forEach(listener => {
    window.removeEventListener('focus', listener.listener);
});

// 移除 visibilitychange 事件监听器
visibilityListeners.forEach(listener => {
    document.removeEventListener('visibilitychange', listener.listener);
});

console.log('All specified event listeners removed.');