Calling Java Script not working in TIMER function

1 
import flash.external.ExternalInterface;

var timer:Timer = new Timer(1000);
timer.addEventListener(TimerEvent.TIMER, blah);
timer.start();
function blah():void {
    
    

     var paramObj:Object =      LoaderInfo(this.root.loaderInfo).parameters.bannerid;
    var someVar:String = new String(paramObj);
    ExternalInterface.call("displayAlert",someVar );
    timer.stop();
    
}

Not Working,what’s wrong?