setwatch doesn't work stable

I have coded a class for this problem. Works great and stable for me. I'm sharing it.

watchClass=function(pin,callback){
    var lastTime=0;
    lastState=1;
    var interval=setInterval(function(){
        currentState=digitalRead(pin);
        currentTime=getTime();
        if (currentState!=lastState) {
            var e={
                state:currentState,
                lastTime:lastTime,
                time:currentTime
            }
            lastTime=currentTime;
            lastState=currentState;
            callback(e);
        }
    },30);
}
pinMode(E2, "input_pulldown");
x=new watchClass(E2,function(e){
console.log(e);
});