EventListener return value is ignored in html bindings

[DartBot]

This issue was originally filed by rice@google.com

---

I am trying to intercept the right-click context menu as follows:

Window _window;
_window.on.contextMenu.add((Event event) {return false; });

This code is in fact called when I click the right mouse button in the browser window, but the 'return false' no longer has the desired effect of preventing the browser context menu from appearing, as it did in the previous DOM bindings.

A cursory inspection of the DOM code shows that contextMenu is a getter on the WindowEvents interface, returning an EventListenerList, and EventListenerList.add takes an EventListener as its first argument. However, EventListener is defined as a void function, while the standard DOM allows a return value in order to provide a way to cancel the event.

[DartBot]

This comment was originally written by drfibonacci@google.com

---

Added Area-UI, Triaged labels.

[dgrove]

Set owner to @jacob314.

[jacob314]

This is by design.

You should use
event.preventDefault() which works fine in Dart as well as JS.

The pattern you are using only works for old style JavaScript element.oneventname listeners and not the more modern JavaScript element.addEventListener listeners which is what the .on event listeners delegate to.

---

Added WontFix label.