handler-use

Assign a .use callback to the handler function that returns an array containing loader(YourLoader). The loader then runs wherever the handler is mounted, and the handler reads the data with ctx.use(YourLoader) inside its body.

handler.use provides the handler's defaults, while explicit use() at the mount site adds overrides. Items merge with handler.use first and explicit use second; accumulating items like middleware run from both, while last-write-wins items like loading() are replaced by the explicit one.

Parallel slots allow only revalidate, loader, loading, errorBoundary, notFoundBoundary, and transition. Middleware and layout are not permitted; returning a disallowed item from handler.use throws a registration error naming the offending type and mount site.

Use the slot descriptor form { handler, use } inside parallel() and put loading() in that descriptor's use callback. The shared parallel use() broadcasts to every slot, but slot-local use is the narrowest scope and wins for last-write-wins items like loading().

No. A bare JSX element passed as a handler has no function to attach properties to, so .use cannot be added. Pass a function handler or a branded Static(), Prerender(), or Passthrough() definition and attach .use to that instead.

Validation runs at registration or first match, not at handler definition time. The same handler mounted in a path() and an intercept() is checked against each mount site's allowed-types set when registered.