📈 Add last-page-visible trigger

[Enriqe]

Closes #22901

[gmajoulet]

Quick question: can't we already do that with the story-page-visible trigger and the PAGE_INDEX + PAGE_COUNT variables?

[Enriqe]

I believe @jeffjose had an explicit request for it to be a trigger, since a variable would be more expensive for publishers. Is that correct Jeff?

[Enriqe]

Oh and also:

He wanted to support sending the story end to different request url. Let's still do different event types : ) Because event is one to one match to request.

You can read more of the discussion in #22901

[jeffjose]

I believe @jeffjose had an explicit request for it to be a trigger, since a variable would be more expensive for publishers. Is that correct Jeff?

AMP Analytics is declarative in nature, with rudimentary support for some evaluations. We cannot do PAGE_INDEX + 1 = PAGE_COUNT.

Even if we did that, it'll be hooked into an enabled switch, which is evaluted on every event which is dropped everytime except the last page.

In short, a) cannot evaluate expressions b) and even if we did it, it'll be expensive.

[gmajoulet]

Awesome, thanks for the context :)