/* mini challenge create an event handler */   
  
var image = document.getElementById("myImage");
// ok
  // image.onclick=changeImage;  
// better
  // image.addEventListener("click" , changeImage , false);  
// much better (notice function below)  
  //  eventListener (image, "click", changeImage);
  
 // cross browser  addEventListener 
 function eventListener (elementName, eventName, functionName){
  if (elementName.addEventListener) {
    // yes, use it
    elementName.addEventListener(eventName, functionName, false);
    return true;
  } else {
    // have to use attachEvent
    elementName.attachEvent("on" + eventName, functionName);
    return true;
  }
}