What is isorouter?

isorouter is a lightweight, framework-agnostic SPA router built on the browser Navigation API.

The interception, matching, guards, lazy-loading and async-commit state machine live in a pure-TypeScript core with zero framework dependencies. Thin adapters bind that core into Svelte 5, React and Vue 3.

@isorouter/core     ← pure TS: matcher, guards, lazy, commit state machine
   ├── @isorouter/svelte   ← createSubscriber bridge
   ├── @isorouter/react    ← useSyncExternalStore bridge
   └── @isorouter/vue      ← shallowRef bridge

Why this shape

The core is an external store: it exposes subscribe(fn) + getSnapshot() and publishes an immutable snapshot with a fresh reference on every commit. That contract is the lowest common denominator across the three reactivity systems — each adapter wraps it with the framework's native primitive:

Framework	Bridge primitive	Why
React	useSyncExternalStore(subscribe, getSnapshot)	Detects change via Object.is(prev, next) — requires a new reference per update.
Svelte 5	createSubscriber(update => subscribe(update))	Subscription is live only while current is read in a reactive scope; auto-torn-down.
Vue 3	shallowRef(snapshot) + subscribe	Snapshot is already immutable, so shallow ref replacement is exactly right.

A Proxy-based core was considered and rejected

A Proxy that mutates in place keeps the same reference, so useSyncExternalStore would never see a change and React would not re-render. The immutable-snapshot contract is what makes one core serve all three frameworks.

Design principles

• The platform does the hard part. Click interception, history entries, scroll restoration and focus are the browser's job via the Navigation API — isorouter orchestrates matching and commits on top, it doesn't reimplement the history stack.
• No History API fallback by design. isorouter targets the Navigation API directly. If you must support pre-2026 engines, load a polyfill before starting the router — see Browser support.
• Type-safety is not bolted on. Declaring routes as const makes navigate reject unknown paths at compile time. See Type-safe navigation.
• Small and tree-shakeable. The core is a single ESM file (~4 KB minified / 1.8 KB gzipped) with zero runtime dependencies and "sideEffects": false.

Next steps

• Installation — pick the package for your framework.
• Quick start — a running router in a few lines.
• Type-safe navigation — the headline TypeScript feature.