var throttle = function(fn, delay, mustRunDelay){
    var timer = null;
    var start;
    // 這裡是利用一個閉包來儲存變數，避免汙染全域性變數
    return function(){
        var context = this,
        args = arguments,
        current = +new Date();
        clearTimeout(timer);
        if(!start){
            // 設定開始時間標記
 

            start = current;
        }
        if(current - start >= mustRunDelay){
            fn.apply(context, args);
            start = current;
        }
        else {
            timer = setTimeout(function(){
                fn.apply(context, args);
            }, delay);
        }
    };
 };