Bun 2.0 Launches Today: Faster JS/TS Dev with Near-Complete Node API

2025-09-10 — The newest release of Bun 2.0 drops today, and it’s less about a single headline feature than a pile of sharp edges that suddenly feel sanded down. You’ll notice it when a fresh project goes from zero to running in seconds, when TypeScript just works without babysitting a compiler, and when bundling feels instant even on a busy laptop. This isn’t a novelty release; it’s the “okay, we can standardize on this” moment.

What’s new (and why it matters)

• Near-complete Node API compatibility: The runtime now covers most Node core modules and edge cases, meaning fewer polyfills and fewer “works on Node, fails on Bun” surprises.
• Windows GA: Windows support is no longer a science experiment—file watching, path handling, and native add-ons feel stable in day-to-day use.
• Faster, smarter bundling: Tree-shaking and incremental builds kick in by default; big TS projects recompile with a blink and hot reload remains responsive under load.
• First-class testing: The built-in runner adds snapshot updates, parallel workers with sane defaults, and tidy failure output that shortens the trip from red to green.
• Plugin ecosystem: Official hooks for macros, loaders, and framework adapters reduce glue code—your bundler config shrinks, your repo gets calmer.

Everyday benefits (measured in minutes, not microseconds)

• Fewer processes to wrangle: Dev server, bundler, test runner, and package manager sit under one roof. Less context switching, fewer “which port is free?” rituals.
• TypeScript without the friction: .ts/.tsx compile in-process; source maps are crisp; strict mode and path aliases behave like you expect.
• npm install (but faster): bun install keeps the lockfile tight and routinely shaves seconds to minutes from cold installs.
• Edge-ready by default: Smaller bundles and fetch-first APIs make it easier to push the same code to functions and edge nodes.

Quick start (15 minutes to shipping something real)

1. Scaffold: bun create app my-app and select your flavor (API, full-stack, SSR, or SPA).
2. Run dev: bun dev starts the server and file watcher—try editing a route or a component and watch hot reload stay calm.
3. Add tests: bun test boots the runner; add a snapshot and see parallel workers chew through suites quickly.
4. Install deps: bun install zod @tanstack/react-query — lockfile updates instantly and your IDE intellisense lights up.
5. Build & preview: bun build and bun preview to sanity-check chunking, env injection, and headers before CI.

Migrate without drama

• Audit Node APIs: List imported core modules; most should map 1:1 in Bun 2.0. Replace legacy shims and mark any CJS-only utilities for later cleanup.
• Env & paths: Move secrets to environment maps; confirm import.meta.url and path aliases resolve the same in build and dev.
• Scripts parity: Mirror npm run tasks with bun run; keep the old scripts for one sprint while CI proves outputs are identical.

Patterns that stick

• Single command UX: Prefer bun dev, bun test, and bun preview over bespoke scripts to reduce onboarding time.
• Contracts first: Use zod/valibot in request boundaries; generate types for your client and tests to keep failing cases obvious.
• Budgeted bundles: Track bundle size and p95 cold start in CI; fail the build if regressions exceed agreed thresholds.
• SSR with cache hints: Pair streaming SSR with micro-caches; revalidate in the background to keep TTFB low at the edge.

Common pitfalls (and the quick fixes)

• ESM/CJS tangles: If a library is CJS-only, prefer an ESM fork or a light shim; avoid dual-transpile pipelines that hide bugs.
• Native add-ons: Rebuild on each platform in CI; cache artifacts per OS/arch to keep your pipeline snappy.
• Implicit globals: Remove Node-specific globals from browser bundles; the new analyzer will warn—treat warnings as blockers.
• Over-eager HMR: If state wipes on every change, tighten your HMR boundaries to components/routes that actually need reloads.

My brief anecdote (when it clicked)

This morning, a teammate pinged me about a flaky integration test that only failed on Windows. I cloned the repo on a Windows laptop, ran bun test, watched the parallel worker isolate the suite, and caught a path separator bug in five minutes. The fix landed with a single snapshot update and a tiny path util. That’s when Bun 2.0 felt less like a fast toy and more like the path of least resistance for real teams.

Who should move first

• Greenfield apps: If you’re starting fresh, the single-tool experience trims days off setup and onboarding.
• DX-hungry teams: Shops that value quick feedback loops, strict type safety, and clean CI will feel the gains immediately.
• Edge & SSR projects: If you deploy close to users, smaller bundles and fetch-centric APIs pay back with lower TTFB.

Bottom line

Bun 2.0 isn’t trying to reinvent the stack; it’s collapsing the stack into fewer moving parts—without giving up the speed that drew people to Bun in the first place. If your team is tired of glue code, split tooling, and cold starts, today’s release is a strong signal to pilot it on a real project and measure the difference for yourself.