防抖

        let time= null;
        document.onmousemove = function (ev) {
            if (time) {
                clearTimeout(time)
            }
            time = setTimeout(() => {
                // fn(ev)
            }, 500)
        )
        };

节流

          let previous= 0;
        document.onmousemove = function (ev) {
                let now = Date.now();
                if (now - previous > 200) {
                    fn(ev);
                    previous = now;
                }
        };