One Release Instead of Two
Concurrent Mode and Suspense power the new Facebook website that’s in active development, so we are confident that they’re close to a stable state technically. We also now better understand the concrete steps before they are ready for open source adoption.
Originally we thought we would split Concurrent Mode and Suspense for Data Fetching into two releases. We’ve found that this sequencing is confusing to explain because these features are more related than we thought at first. So we plan to release support for both Concurrent Mode and Suspense for Data Fetching in a single combined release instead.
We don’t want to overpromise the release date again. Given that we rely on both of them in production code, we expect to provide a 16.x release with opt-in support for them this year.
An Update on Data Fetching
While React is not opinionated about how you fetch data, the first release of Suspense for Data Fetching will likely focus on integrating with opinionated data fetching libraries. For example, at Facebook we are using upcoming Relay APIs that integrate with Suspense. We will document how other opinionated libraries like Apollo can support a similar integration.
In the first release, we don’t intend to focus on the ad-hoc “fire an HTTP request” solution we used in earlier demos (also known as “React Cache”). However, we expect that both we and the React community will be exploring that space in the months after the initial release.
An Update on Server Rendering
We have started the work on the new Suspense-capable server renderer, but we don’t expect it to be ready for the initial release of Concurrent Mode. This release will, however, provide a temporary solution that lets the existing server renderer emit HTML for Suspense fallbacks immediately, and then render their real content on the client. This is the solution we are currently using at Facebook ourselves until the streaming renderer is ready.
Why Is It Taking So Long?
We’ve shipped the individual pieces leading up to Concurrent Mode as they became stable, including new context API, lazy loading with Suspense, and Hooks. We are also eager to release the other missing parts, but trying them at scale is an important part of the process. The honest answer is that it just took more work than we expected when we started. As always, we appreciate your questions and feedback on Twitter and in our issue tracker.