/**
 * 節流函數
 * @param method 事件觸發的操作
 * @param mustRunDelay 間隔多少毫秒需要觸發一次事件
 */
function throttle(method, mustRunDelay) {
    let timer,
        args = arguments,
        start;
    return function loop() {
        let self = this;
        let now = Date.now();
        if(!start){
            start 
 
= now;
        }
        if(timer){
            clearTimeout(timer);
        }
        if(now - start >= mustRunDelay){
            method.apply(self, args);
            start = now;
        }else {
            timer = setTimeout(function () {
                loop.apply(self, args);
            }, 
 
50);
        }
    }
}
window.onscroll = throttle(function () {
    let scrollTop = document.body.scrollTop || document.documentElement.scrollTop;
    console.log(‘滾動條位置：‘ + scrollTop);
},800)

js防抖節流封裝