Should we be optimistic or pessimistic with UI updates on AJAX requests?

1. What is optimistic UI?
2. What does optimistic update mean?
3. What is optimistic rendering?
4. What is pessimistic rendering?

What is optimistic UI?

Optimistic UI is a pattern that you can use to simulate the results of a mutation and update the UI even before receiving a response from the server. Once the response is received from the server, the optimistic result is thrown away and replaced with the actual result.

What does optimistic update mean?

An optimistic UI update is an update in the user interface showing the final result even before the change requested to the server has returned a success. In other words, the UI changes to the result even before receiving a response from the server.

What is optimistic rendering?

In optimistic UI you don't keep the user waiting for a response. instead you make the assumption that the response will succeed, and provide them with the appropriate response right away. So if a user is posting a comment, or sending a message, you render the view of the content immediately.

What is pessimistic rendering?

Pessimistic rendering boil down to is whether or not events on a page happen before or after they fetch information to and from the database.