delegate except when you cannot use
Event delegation is a technique used to improve application performance. It drastically reduces the number of event subscriptions by leveraging the “bubbling” characteristic of most DOM events. With event delegation, handlers are not attached to individual elements. Instead, a single event handler is attached to a top-level node such as the body element. When an event bubbles up to this shared top-level handler the event delegation logic calls the appropriate handler based on the event’s target.
To find out if event delegation can be used with a particular event, google
mdn [event name] event. In fact, preceding any web platform related google search with
mdn often returns a high quality result from the Mozilla Developer Network. Once you’re on the event’s MDN page, check whether the event
bubbles. Only events that bubble can be used with Aurelia’s
delegate binding command. The
unload events do not bubble so you’ll need to use the
trigger binding command to subscribe to these events.
Here’s the MDN page for blur. It has further info on event delegation techniques for the blur and focus events.
Exceptions to the general guidance above:
trigger on buttons when the following conditions are met:
- You need to disable the button.
- The button’s content is made up of other elements (as opposed to just text).
This will ensure clicks on disabled button’s children won’t bubble up to the delegate event handler. More info here.
click in certain iOS use-cases:
iOS does not bubble click events on elements other than
select. If you’re subscribing to
click on a non-input element like a
div and are targeting iOS, use the
trigger binding command.
More info here and here.