Error and loading states are the design

Empty, loading, partial, error, offline, forbidden, and the one with four thousand rows. Every one of those is a screen someone will see, and in most projects the mockups cover exactly one of them. The states are not edge cases, they are a majority of the states in which your interface exists on a bad connection.

A loading state should occupy the same space as the content it replaces. A skeleton with the right dimensions means nothing moves when the data lands, and nothing moving means nobody misses a tap. A spinner in the centre of an empty box means the entire page jumps when it resolves, which is worse than showing nothing at all.

An error state has one job: say what happened and what to do next. "Something went wrong" achieves neither. "We could not load your invoices: retry, or contact support with reference 4f2a" gives an action and a thread to pull. And it needs to be recoverable in place: an error boundary with a reset that retries the segment beats one that only offers a full reload.