Kanasansoft Web Lab.

var xGround=function(listeners){
    var interval=100;
    var preTime=new Date().getTime();
    var preStatus=null;
    var timer=function(){
        var nowTime=new Date().getTime();
        var xGround=(Math.abs(nowTime-preTime-interval)<100)?"fg":"bg";
        var switchFlag=((preStatus||xGround)!==xGround);
        switch(true){
        case (xGround==="fg")&&switchFlag:
            listeners.switchForeGround&&listeners.switchForeGround();
        case (xGround==="fg"):
            listeners.foreGround&&listeners.foreGround();
            break;
        case (xGround==="bg")&&switchFlag:
            listeners.switchBackGround&&listeners.switchBackGround();
        case (xGround==="bg"):
            listeners.backGround&&listeners.backGround();
            break;
        }
        preTime=nowTime;
        preStatus=xGround;
    };
    setInterval(timer,interval);
};
var obj={
    switchForeGround:function(){console.log("switch foreground");},
    switchBackGround:function(){console.log("switch background");},
    foreGround:function(){console.log("foreground");},
    backGround:function(){console.log("background");}
};
xGround(obj);