Thank you Thomas and Colin. Setting onpopstate with a lambda is perfect!
On Thursday, 5 December 2024 at 6:51:23 am UTC+11 Thomas Broyer wrote:
> On Wednesday, December 4, 2024 at 5:10:32 PM UTC+1 Colin Alworth wrote:
>
> Note that "@FunctionalInterface" is not required to express a Java
> interface with only one abstract method as a lambda. You can write:
>
> DomGlobal.window.onpopstate = event -> {
> // Do something
> return null;
> };
>
> to use it as a lambda. This compiles for me with GWT 2.12.1 and Java 11.
>
>
> Does it show that I haven't written that kind of code for quite some
> time? 😂
> (and/or rely too much on my IDE)
>
>
> The key is the "return null", missing in your example (and in Thomas's as
> well as a return type for the anon inner class).
>
> The return type is declared as Object, which may be an oversight in the
> original closure externs file, I don't see a way that an event handler can
> change anything by returning a different value. In JS, a missing return
> would implicitly return undefined, but Java requires an explicit return for
> non-void methods.
>
>
> An event handler's return type is used to cancel the event (
> https://blog.ltgt.net/html-event-handlers/#return-value /
> https://html.spec.whatwg.org/multipage/webappapis.html#the-event-handler-processing-algorithm),
>
> but for that specific event it doesn't matter as it's not cancelable anyway
> (
> https://html.spec.whatwg.org/multipage/browsing-the-web.html#updating-the-document:popstateevent
> )
>
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