tanstack-router-preload

name	tanstack-router-preload
description	TanStack Router's `defaultPreload: "intent"` policy for snapmatch — modulepreload of route JS chunks plus loader execution on `touchstart`/hover, independent from the future Workbox SW plan. Triggers on: defaultPreload, modulepreload, intent preload, viewport preload, link preload, tanstack router preload, route preload.
license	MIT

Sub-skill of tanstack. Owns the project's preload policy: defaultPreload: "intent" is set in getRouter() and every <Link> in apps/example-game/app/ warms its target on hover or touchstart. The repository currently emits no service worker, so preload stands alone; a future Workbox precache would be a separate additive layer. Preloading is the SPA-runtime optimization that complements the SSG build output.

When to invoke

• Editing defaultPreload in apps/example-game/app/router.tsx or the matching turbo/generators/templates/app/app/router.tsx.
• Authoring or reviewing a <Link preload="intent" | "viewport" | "render" | false> per-link override.
• Diagnosing a slow first-click navigation (the route loader, not the chunk fetch, is usually the lag; the current app has no service worker).
• Deciding whether to bump defaultPreloadStaleTime (default: don't).
• Anyone proposing quicklink, react-quicklink, or a <link rel=prefetch> polyfill — the answer lives here.

Owns

The project-wide defaultPreload value, the per-<Link> override pattern, the iPad/touchstart rationale for intent over viewport, and the boundary between shipped preload behavior and a future additive Workbox layer.

Defers to

• tanstack (parent) — version pin and dispatch.
• tanstack-router-routing — for the <Link> API itself; the preload prop value is owned here, but the <Link> surface (typed to, params, search, Register declaration) lives there.
• tanstack-router-pwa-deep-links — for the explicitly future, currently unshipped SW contract.
• tanstack-start-spa-prerender — for what the SSG output looks like (prerendered shell + per-route chunks). This skill consumes that output's chunk graph.
• playwright-conventions — for the load-bearing ASK-FIRST rule before any preload-behavior verification test.

Snapmatch stack rules

• SSG describes the build; SPA describes the runtime. Snapmatch ships static HTML/JS/CSS to Firebase Hosting (SSG), but every navigation is client-side via TanStack Router (SPA). defaultPreload operates at the SPA-runtime layer: it preloads the route's code-split JS chunk via <link rel=modulepreload> and runs the route's loader early. It does not prefetch HTML — there is no per-route HTML to prefetch beyond the prerendered shell.
• No shipped Workbox layer yet. The current build emits no service worker. If the separately gated PWA work lands, its precache will complement rather than replace route preload; do not document that future layer as current behavior.
• quicklink was considered and rejected. quicklink (and the abandoned react-quicklink wrapper) prefetches <link rel=prefetch> for visible link hrefs — the HTML at the URL. In this SPA runtime, Firebase Hosting already routes URLs to the same shell; HTML prefetch is redundant even without a service worker. The right primitive is modulepreload of the route chunk + loader execution on intent — exactly what defaultPreload: "intent" does. Do not reintroduce quicklink.
• iPad reason for intent over viewport. intent fires on touchstart (iOS) and mouseenter (desktop) — only the link the user is about to tap, ~100ms before the click. viewport fires when the link enters the viewport; on a 12.9" iPad, that can mean a dozen visible links per scroll, warming chunks the user will never tap and wasting battery and bandwidth. intent is the project default; promote a link to viewport only when a hero/primary action genuinely warrants it.
• Pillar 4 (CLI-gate-first): defaultPreload's value is typed by TanStack Router as 'intent' | 'viewport' | 'render' | false. A typo fails tsgo --noEmit for free. Same applies to per-<Link> preload props.

Patterns

Project default — already wired

// apps/example-game/app/router.tsx — pinned: @tanstack/react-router ^1.x
import { createRouter as createTanStackRouter } from "@tanstack/react-router";
import { routeTree } from "./routeTree.gen";

export function getRouter() {
  return createTanStackRouter({
    routeTree,
    scrollRestoration: true,
    defaultPreload: "intent",
  });
}

This is the project-wide policy. Every <Link> inherits intent unless its own preload prop overrides it. The same option is set in turbo/generators/templates/app/app/router.tsx so a freshly generated app starts with the same policy.

Per-link override

import { Link } from "@tanstack/react-router"; // see `tanstack-router-routing`

// Hero CTA — warm the chunk as soon as it scrolls into view.
<Link to="/games/sample/$level" params={{ level: 1 }} preload="viewport">
  Start the sample
</Link>

// Heavy / rarely-clicked link — opt out entirely.
<Link to="/about" preload={false}>About</Link>

// Aggressive — preload on first render. Use sparingly; defeats code-splitting if overused.
<Link to="/games" preload="render">All games</Link>

Override values: 'intent' | 'viewport' | 'render' | false. Default to project-intent; document the reason next to any override.

defaultPreloadStaleTime — leave at default

TanStack Router caches preloaded route data for a short window; a click within that window reuses the warm result. Tune only if a Playwright run shows a stale loader result reaching the user. Default is fine for IDB-backed loaders — state changes propagate via the BroadcastChannel re-hydration path owned by idb, not via stale-timer expiry.

Verifying a preload fired (manual)

DevTools → Network → "JS" filter; hover a <Link> (or touchstart on iPad over LAN) — a <link rel=modulepreload> for the next route's chunk appears before the click event. If it doesn't fire, either: (a) the route's chunk is already in the initial bundle (no preload needed), (b) the link is preload={false}, or (c) the Register declaration is missing from router.tsx and <Link> fell back to plain <a> (see tanstack-router-routing).

Anti-patterns

• Don't set defaultPreload: "viewport" as the project default. iPad scroll would warm every visible link; intent is the right default. Per-link viewport for a single hero CTA is fine.
• Don't set defaultPreload: "render" as the project default. Renders every route's chunk on initial paint — defeats code-splitting and bloats first-paint.
• Don't introduce quicklink / react-quicklink / a <link rel=prefetch> polyfill. The router primitive is the right tool for this stack; HTML prefetch is redundant with the SW precache. See "Snapmatch stack rules" above.
• Don't preload routes the user can never reach from the current view. Per-link preload={false} for off-flow admin or debug links keeps the chunk graph honest.
• Don't useMemo around <Link> to avoid re-preload. The Compiler memoizes (see react-compiler-rules); manual memo is noise.
• Don't skip the Register declaration in router.tsx. Without it, <Link> falls back to <a> and the preload never fires. See tanstack-router-routing.
• Don't write a Playwright test for preload behavior without asking the user first. Surface structural choices (story-level vs app-level, fixture, what to assert — <link rel=modulepreload> DOM presence vs. timing, reduced-motion) and wait for the answer; ASK FIRST is load-bearing (see playwright-conventions).

Triggers on

defaultPreload, modulepreload, intent preload, viewport preload, link preload, tanstack router preload, route preload