return value type in prepareUpdate

[dakom]

The official renderers seem to generally return a const of {} in prepareUpdate, for example here: https://github.com/facebook/react/blob/master/src/renderers/art/ReactARTFiberEntry.js#L493

While the tutorial at https://github.com/nitin42/Making-a-custom-React-renderer/blob/master/part-one.md suggests to return true

What is the nature of the return type from prepareUpdate and how does it affect commitUpdate() ?

[iamdustan]

The DOM renderer is the only one currently using prepareUpdate. It allows React to compute the new props to apply separately from applying the diff (commit). This is useful for pausing and resuming work. The other renderers compute the diff during reconciliation.

It was added in #8607 which has substantially more information on the motivation and use case.

[gaearon]

The other renderers compute the diff during reconciliation.

Not sure what you meant by this—prepareUpdate does fire during reconciliation. We compute updates during reconciliation but don’t commit them yet. This makes it possible to split reconciliation across frames. Then we commit the whole tree at once when it is ready.

[gaearon]

I added a non-exhaustive reference here.

https://github.com/facebook/react/tree/master/packages/react-reconciler#an-incomplete-reference