JS之移除事件的兼容性处理

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        window.onload = function () {
            // 移除事件的兼容性处理
            function removeEventListener(ele, eventType, fn) {
                // 判断当前浏览器是否支持removeEventListener方法
                if (ele.removeEventListener) {
                    ele.removeEventListener(eventType, fn);
                } else if (ele.detachEvent) {
                    ele.detachEvent('on' + eventType, fn);
                } else {
                    ele['on' + eventType] = null;
                }
            }
            
            var btn = document.getElementById('btn');
            function fn() {
                alert('你好');
                removeEventListener(btn, 'click', fn);
            }
            btn.addEventListener('click', fn);
        }
    </script>
</head>
<body>
<input type="button" value="点击" id="btn">
</body>
</html>