<!DOCTYPE html>
<html>
    <head>
        <meta charset=utf-8>
    </head>
    <body>
    	
        <script type="text/javascript">
            let count = 0
            const _proxy = object => {
                // 补全代码
                return new Proxy(object, {
                    get(target, property){
                        property in target ? count++ : count--
                    }
                })
            }
        </script>
    </body>
</html>