中央定时器控制

var timer = {
        timerId : 0,
        timers : [],
        
        add : function(fn){
            this.timers.push(fn);
        },
        
        start : function(){
            if(this.timerId){
                return;
            }
            (function runNext(){
                if(timer.timers.length > 0){
                    for(var i = 0; i < timer.timers.length; i++){
                        if(timer.timers[i]() === false){
                            timer.timers.splice(i,1);
                            i--;
                        }
                    }
                    timer.timerId = setTimeout(runNext,0);
                }
            })();
        },
        
        stop : function(){
            clearTimeout(this.timerId);
            this.timerId = 0;
        }
};