Checking existence of properties in JavaScript

Question

I\'m new to JavaScript and a little bit confused with the duck typing concept. As far as I can tell, I understood the concept. But that leads to a strange consequence in my thou

Answer 1

As you are using a specific framework to capture your events, i think that you should assume that the originalEvent is always defined. If it isn't, then it is probably a good thing to throw an error as something clearly went wrong somewhere in the capture of the event.

However, the event could be a MouseEvent or a TouchEvent, also, the webkitForce property may not be supported. These are the kind of cases that you might want to detect :

// assume that originalEvent is always be defined by jQuery
var originalEvent = e.originalEvent.originalEvent;
if (originalEvent instanceof TouchEvent) {  // if touch events are supported
  // the 'touches' property should always be present in a TouchEvent
  var touch = originalEvent.touches[0];
  if (touch) {
      if (touch.webkitForce) {
        // ...
      } else {
        // webkitForce not supported
      }
  }  // else no finger touching the screen for this event
} else {
   // probably a MouseEvent
}