URLRouter

libwasm.router is the client router. It is experimental, it is not SvelteKit, and svelte-d uses only the patterns it can express. Layouts are not router entries. They stay mounted as @child wrappers; the page is swapped in the entering callback. goto / invalidate / beforeNavigate / prefetch / true hydration (attach handles to existing SSR DOM) are titled seams. Until those exist, do not print APIs that call them.

Match language

A route pattern is a string. Matching walks the URL and the pattern in lockstep:

• Literal segments must match exactly.
• :name consumes one path segment and stores it in RouterEvent.parameters["name"].
• Trailing * matches the rest and succeeds immediately.
• At most 64 placeholders (maxRouteParameters).
• Specificity is static chars ≫ :param ≫ *. Kit uses that so /:slug does not steal /admin.

RouterEvent carries parameters, prevURL, and newURL. Callbacks have type Optional!(Promise!void) delegate(ref RouterEvent ev). Empty optional means “continue now.” A D Promise!void means “call iterate again when it fulfills.” That promise is in-process, not a JsPromise.

Direction and UDAs

enum Direction { Entering, Leaving, Always }
 
@entering!"/admin/users/:id"
Optional!(Promise!void) enterUser(ref RouterEvent ev) { /* applyKitParams */ }
 
@leaving!"/admin/users/:id"
Optional!(Promise!void) leaveUser(ref RouterEvent ev) { /* … */ }

registerRoutes (generated on the struct, called from _start after compile!) walks those UDAs and registers them. svelte-d prints @entering on the page struct from the kit file path: src/routes/admin/users/[id]/+page.svelte → /admin/users/:id. Groups (app) strip. [[optional]] expands to two registrations. [...rest] becomes trailing * and loses the name.

navigateTo and the browser

URLRouter constructs a ManagedPool(64*1024), calls setupRouter(), and exports a JS-callable delegate named "navigate_to". The engine’s libwasm.ts / debug-bridge.ts listen for popstate and callNative('navigate_to', location.pathname). The wasm-eh onpopstate UDA is not reliable, which is why that JS path exists.

navigateTo does not pushState when document().location().pathname already matches. Leaving drops the route from m_activeRoutes, so a later visit (back/forward) still fires @entering even if the route was seen before. Kit setVisible + applyKitParams depend on that re-fire, including /users/:id param changes while the pattern is still the same.

If a navigation starts while callbacks are still pending, the new URL is stored as m_pendingURL and run when the iterator finishes. setTitle / getTitle and setBasePath / getBasePath are the other knobs. Default _start without ready is router().navigateTo(document().location().front.pathname()).

What svelte-d prints

One page @entering per path. Static segments beat params. Layouts stay mounted. The page struct is remounted or setVisibled inside the entering callback (KitRoutes). There is one wasm module. A second mixin Spa per layout would be a second DOM.

This router and vibe.0’s URLRouter share a match language (:name, *, 64 placeholders) on purpose, so a kit [id] is :id on both cells. They are still two types in two packages. Do not import vibe.http.router from lang=d.