JS函数节流代码实现

var throttle=function(fn,interval){
    var _self=fn; //保存需要被延长执行的函数引用
    var timer;
    var firstTime=true;   //是否是第一次调用

    return function (){
        var args=arguments;
        var _this=this;
        if(firstTime){  //如果第一次调用，不需要延迟执行
            _self.apply(_this,args);
            return firstTime = false;
        }
        if(timer){  //如果定时器还在，说明前一次延迟执行还没有完成
            return false;
        }
        timer = setTimeout(function(){  //延迟一段时间执行
            clearTimeout(timer);
            timer=null;
            _self.apply(_this,args);
        },interval || 500);
    };
};

var throttle2 = function (callback, delay, trailingTimeout) {
    var leadingCall = false,
        trailingCall = false,
        lastCallTime = 0;

    function resolvePending() {
        if (leadingCall) {
            leadingCall = false;
            callback();
        }
        if (trailingCall) {
            proxy();
        }
    }

    function timeoutCallback() {
        requestAnimationFrame(resolvePending);
    }

    function proxy() {
        var timeStamp = Date.now();
        if (leadingCall) {
            if (timeStamp - lastCallTime < trailingTimeout) {
                return;
            }
            trailingCall = true;
        } else {
            leadingCall = true;
            trailingCall = false;
            setTimeout(timeoutCallback, delay);
        }
        lastCallTime = timeStamp;
    }
    return proxy;
};