Using the handleEvent callback function

You can also use listener objects that support a handleEvent function. Regardless of the name of the event that is broadcast, the listener object's handleEvent method is called. You must use an if..else or a switch statement to handle multiple events. For example, the following code uses an if..else statement to handle the click and change events:

// define the handleEvent function
// pass it evt as the event object parameter

function handleEvent(evt){
    // check if the event was a click
    if (evt.type == "click"){
        // do something if the event was click
    } else if (evt.type == "change"){
        // do something else if the event was change
    }
};

// register the listener object to 
// two different component instances
// because the function is defined on 
// "this" object, the listener is this.

instance.addEventListener("click", this);
instance2.addEventListener("change", this);