Detecting iBeacons UUID using android-altbeacon-module

Hello , I am try to create app that scans for ibeacons near to him by using android-altbeacon-module but i can not understand it clearly .. any one has ant idea ?? Thanks . This is my code

function startScan(e) {
    if (TiBeacons != null) {
        TiBeacons.addEventListener("enteredRegion", enteredRegionCallback);
        TiBeacons.addEventListener("exitedRegion", exitedRegionCallback);
        TiBeacons.addEventListener("determinedRegionState", rangingCallback);
 
        TiBeacons.startRangingForBeacons({
            identifier : null,
            uuid : null,
            major : null,
            minor : null
        });
 
    }
 
}