Not necessarily, if the list is loaded only after the user clicks in the button, there may be a delay until it is displayed to the user (having it preloaded would mitigate that delay, I think). Another alternative would be to load (before the click) just a few chapters which are near the current one (e.g. 5 previous chapters and 5 subsequent chapters), and present the user the option to "load more..." or "see all..." (then load the whole list when this option is clicked)

Anyway, what about users without JavaScript?

I do not understand well about cache, so I do not know if your option is better, but we could also:
1.Load ("after" the click) just a few chapters which are near the current one
(e.g. 5 previous chapters and 5 subsequent chapters)
2.Present the option to "load more..." or "see all..." (then load the whole list when this option is clicked).

Anyway, the points are:

1. Do not be slow to load the whole page in case of big books
2. Do not be slow to load the menu (when clicked).

molly.white5 wrote:

We're going to improve load times by caching the JSON objects. This should improve performance without causing a delay in loading the dropdown or requiring additional requests to be sent.