feat: add isServer by schiller-manuel · Pull Request #4648 · TanStack/router

schiller-manuel · 2025-07-13T22:50:54Z

Summary by CodeRabbit

New Features
- Router now respects an optional runtime isServer override for consistent server/client behavior across frameworks, preserving existing SSR/CSR flows.
Chores
- Introduced a small support package providing per-environment isServer values and adjusted test/build resolution to favor a development variant during test runs.

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nx-cloud · 2025-07-13T22:51:18Z

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☁️ Nx Cloud last updated this comment at 2026-01-24 10:27:32 UTC

pkg-pr-new · 2025-07-13T22:55:49Z

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commit: fabb267

nick-potts · 2025-07-14T15:48:56Z

Is there a way to override this in the router config?

schiller-manuel · 2025-07-14T16:43:56Z

@nick-potts no. what would you need this for?

coderabbitai · 2026-01-24T09:02:31Z

📝 Walkthrough

Walkthrough

Adds a new package @tanstack/router-is-server exporting environment-specific isServer values and updates router core and framework integrations to prefer (isServer ?? router.isServer) for server/client detection across SSR, hydration, loaders, transitions, and scroll restoration.

Changes

Cohort / File(s)	Summary
New package: router-is-server `packages/router-is-server/package.json`, `packages/router-is-server/tsconfig.json`, `packages/router-is-server/vite.config.ts`, `packages/router-is-server/eslint.config.js`	Add package scaffolding, multi-environment exports (server=true, client=false, development=undefined), build/test config, and lint overrides.
router-is-server sources `packages/router-is-server/src/server.ts`, `packages/router-is-server/src/client.ts`, `packages/router-is-server/src/development.ts`	Three entry modules exporting `isServer` with env-specific values (true / false / undefined).
Core: re-export & dependency `packages/router-core/package.json`, `packages/router-core/src/isServer.ts`, `packages/router-core/src/index.ts`	Add dependency on `@tanstack/router-is-server`, introduce `isServer` re-export on router-core public API.
Core logic updates `packages/router-core/src/router.ts`, `packages/router-core/src/load-matches.ts`, `packages/router-core/src/scroll-restoration.ts`, `packages/router-core/src/isServer.ts`	Import and use `(isServer ?? this.isServer)` across history init, origin detection, loader/preload/hydration logic, SSR branches, and scroll restoration guards.
React integrations `packages/react-router/src/...` (`Asset.tsx`, `Match.tsx`, `Matches.tsx`, `ScriptOnce.tsx`, `scroll-restoration.tsx`), `packages/react-router/vite.config.ts`	Import `isServer` and replace `router.isServer` checks with `(isServer ?? router.isServer)` in SSR/hydration, pending/error rendering, script emission; add Vite resolve condition for tests.
Solid integrations `packages/solid-router/src/...` (`Asset.tsx`, `Match.tsx`, `Matches.tsx`, `ScriptOnce.tsx`, `Transitioner.tsx`, `scroll-restoration.tsx`), `packages/solid-router/vite.config.ts`	Same pattern: prefer `isServer` when defined for SSR/no-SSR gates and test-time resolution.
Vue integrations `packages/vue-router/src/...` (`Asset.tsx`, `Match.tsx`, `Matches.tsx`, `ScriptOnce.tsx`, `Transitioner.tsx`, `scroll-restoration.tsx`), `packages/vue-router/vite.config.ts`	Same pattern applied to Title/Script, pending promise creation, transition and scroll logic; Vite test resolve adjustments.
SSR query integration `packages/router-ssr-query-core/src/index.ts`	Use `(isServer ?? router.isServer)` for SSR detection in SSR-query glue code.
Framework misc files `packages/*-router/src/Asset.tsx`, `Match.tsx`, `Matches.tsx`, `ScriptOnce.tsx`, `Transitioner.tsx`, `scroll-restoration.tsx`	Broad update across framework adapters to coalesce `isServer` with router server flag.
Config & tooling `packages/*-router/vite.config.ts`, `labeler-config.yml`	Add test-time resolve.condition overrides for VITEST and labeler entry for new package.

Sequence Diagram(s)

sequenceDiagram
    participant Component
    participant isServerModule as isServer (module)
    participant Router
    participant Env as Server/Browser

    Component->>isServerModule: import isServer
    Component->>Router: read router.isServer
    Component->>isServerModule: evaluate (isServer ?? router.isServer)
    alt resolved true
        Component->>Env: run server-branch (SSR render)
    else resolved false
        Component->>Env: run client-branch (hydrate/mount)
    else resolved undefined
        Component->>Router: fallback to router.isServer decision
        Router->>Env: run appropriate branch
    end

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Possibly related PRs

fix(solid-router): dev server hydration with pending component #5585: Modifies Match server/no-SSR fallback logic (related changes to pending rendering and server-detection).
fix(router): prevent script tag duplication in SSR and client-side navigation #5095: Changes Asset/Script handling and client guards (overlaps with script emission and hydration guards).
feat: cache routeTree on the server in-between requests #6475: Modifies router internals around server-detection and route initialization (overlaps with core router.ts edits).

Suggested reviewers

birkskyum

Poem

🐰 I nibble code beneath the moon,
I bring isServer — true or false or soon.
Servers shout "true", browsers hum "no",
Tests can pause with undefined glow.
Hop, hydrate, render — off we go! 🥕

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 28.57% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'feat: add isServer' accurately describes the main change: introducing a new isServer feature across the codebase.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

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coderabbitai

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@packages/react-router/vite.config.ts`:
- Around line 8-12: The Vite config currently unconditionally sets
resolve.conditions to an empty array when VITEST is unset, which overrides
Vite's defaults; change the resolve block so that the conditions property is
only added when process.env.VITEST is truthy (use ['development'] then) and omit
or leave conditions undefined for non-test builds so Vite's default resolution
is preserved; update the resolve object where "conditions" is set in the vite
config (refer to resolve.conditions and process.env.VITEST) to only supply the
conditions key during test runs.

packages/react-router/vite.config.ts

Sheraff · 2026-01-24T09:12:59Z

packages/start-plugin-core/src/plugin.ts

+              define: {
+                // Replace __TSR_IS_SERVER__ with false for client builds
+                // This enables tree-shaking of server-only code branches
+                __TSR_IS_SERVER__: 'false',
+              },


I don't think I saw this variable anywhere, it is a remainder of a previous attempt?

github-actions bot added package: react-router package: router-core package: solid-router labels Jul 13, 2025

schiller-manuel mentioned this pull request Jul 13, 2025

fix(solid-router): prevent client effects running on server #4621

Merged

schiller-manuel force-pushed the is-server branch from 451a556 to 5140f74 Compare January 24, 2026 09:02

github-actions bot added package: start-plugin-core package: router-ssr-query-core package: vue-router labels Jan 24, 2026

schiller-manuel force-pushed the is-server branch from 5140f74 to b465d43 Compare January 24, 2026 09:04

coderabbitai bot reviewed Jan 24, 2026

View reviewed changes

packages/react-router/vite.config.ts Outdated Show resolved Hide resolved

Sheraff reviewed Jan 24, 2026

View reviewed changes

schiller-manuel force-pushed the is-server branch from b465d43 to 2941924 Compare January 24, 2026 09:36

schiller-manuel added 3 commits January 24, 2026 10:43

feat: add is-server

db362a9

clean lint config

4b695ff

resolve conditions

16d8f81

schiller-manuel force-pushed the is-server branch from eae4e68 to 16d8f81 Compare January 24, 2026 09:43

fix workerd export condition

c6e587a

schiller-manuel force-pushed the is-server branch from 4355b76 to c6e587a Compare January 24, 2026 10:15

ci: apply automated fixes

fabb267

schiller-manuel merged commit e79ad7e into main Jan 24, 2026
6 checks passed

schiller-manuel deleted the is-server branch January 24, 2026 10:28

elithrar mentioned this pull request Jan 24, 2026

@tanstack/router-is-server not published to npm - breaks 1.157.0 installs #6483

Closed

This was referenced Jan 24, 2026

refactor: no additional package for isServer #6485

Merged

fix: re-export correctly #6489

Merged

performance: no reactivity on the server #6497

Merged

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feat: add isServer#4648

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