allow SDK users to subscribe to changes

[barteksekula]

Not sure if that's the right place and you are open to feedback right now, but just wanted to send you this idea:

Maybe instead of always running window.reload we could let users decide what they want to do?
Something like this https://github.com/episerver/cms-visual-builder-hello-world/blob/088ac8d34abb6408829c9d0165b506bdc9931abd/src/helpers/onContentSaved.ts#L34
instead of

content-js-sdk/packages/optimizely-cms-sdk/src/preview/react/PreviewComponent.tsx

Line 31 in bf8fa6b

window.location.replace(finalUrl);

?

I mean the SDK can be used in a server-side rendered app (nextjs, remix etc) but also in a traditional SPA.

[JohanPetersson]

Always open to feedback! Using the preview component is optional, of course, and the idea is to add more capabilities to it. For example, we will look into optimistic client-side updates, so we don't have to refresh the whole page, just the changed property. This behavior could be controlled by an attribute data-opti-on-change="refresh|optimistic|none" (by traversing the DOM and find the nearest occurrence from the changed property).

In its current state, not sure how much value we would add with an (optional) callback function. Adding your own event listener is probably as easy. But when/if we add more capabilities, it probably makes sense to have a callback so you can have better control over the optimistic client-side updates.