Case Study Details Pitfalls of Running Next.js on Bun
A new case study explores the practical challenges of running Next.js applications on the Bun runtime instead of Node.js. While acknowledging Bun's performance benefits, the author highlights issues with module resolution, incomplete polyfills, and native binding incompatibilities that require significant compatibility testing for production use.
- Vercel introduced public beta support for the Bun runtime for its Functions product in late 2025, allowing developers to switch from Node.js by adding `"bunVersion": "1.x"` to their `vercel.json` file. Internal Vercel tests showed Bun reduced average latency by 28% for CPU-bound Next.js rendering workloads compared to Node.js. - Despite general speed improvements, a January 2026 benchmark by Platformatic comparing Next.js runtimes on AWS EKS found Bun had significantly higher average and p99 latencies (246ms and 974ms, respectively) compared to Node.js (20ms and 174ms) and Deno (11-14ms and 101ms). - Bun is designed as an all-in-one toolkit to replace the fragmented toolchain, integrating a runtime, package manager, bundler, and test runner into a single binary. It is built on JavaScriptCore, the engine used by Safari, and written in the Zig programming language. - The WinterCG (Web-interoperable Runtimes Community Group) is a key initiative working to standardize APIs across different server-side JavaScript environments like Node.js, Deno, and Cloudflare Workers. This effort aims to ensure that frameworks like Next.js can be written once and run seamlessly across various platforms, reducing runtime-specific compatibility issues. - Developers have encountered compatibility issues when using Bun with Next.js's Turbopack bundler, with one reported case involving the AWS SDK failing to import and crashing the build. Workarounds for such issues can involve using Bun's global namespace for its APIs (e.g., `Bun.SQL()`) instead of direct imports. - For incompatibilities within third-party libraries, Bun provides a `bun patch` feature that allows developers to modify a dependency's code locally and create a persistent patch file to fix the issue. - The Bun team runs thousands of tests from the official Node.js test suite before every release and considers it a bug if an npm package works in Node.js but not in Bun. However, some Node.js modules like `node:v8` and `node:module` remain only partially implemented. - On Windows, developers have reported `ENOENT` errors when creating a Next.js app directly with Bun, caused by a race condition where Bun attempts to read files before the OS has finished writing them. The recommended workaround is to initialize the project with `npx create-next-app` and then switch to Bun for installing dependencies and running the dev server.
