The cost of switching JavaScript runtimes in 2026

Bun delivers the highest throughput and lowest cold start costs

Bun reaches 94,000 requests per second in HTTP throughput tests for a simple JSON endpoint. This outperforms Deno at 52,000 requests per second and Node.js at 31,000 requests per second. In production environments with actual database queries and business logic, the performance gap between Bun and its competitors narrows to 20-30 percent because the real bottleneck is the PostgreSQL connection pool. Serverless cold start times favor Bun at 45ms, compared to 95ms for Deno and 180ms for Node.js. These millisecond differences translate to direct savings. One company saved 3,000 dollars per month by migrating AWS Lambda functions from Node.js to Bun. Bun uses JavaScriptCore and Zig for native code to achieve these speeds. Bun’s Bun.file() API performs file operations 2-3 times faster than the Node.js fs module. Node.js runs on the V8 engine and relies on decades of optimization. Deno also uses the V8 engine but utilizes Rust for native bindings. This architecture introduces some overhead for permission checks, though users can disable permissions in production to recover performance. Debugging Bun can be difficult because its profiling tools are less polished than Node.js tools like Chrome DevTools or clinic.js. You should prioritize Bun when you build CLI tools, build scripts, or serverless functions where cold starts matter. Teams should avoid Bun for core business logic with exotic dependencies or systems with complex native module requirements.

Compatibility and TypeScript configuration overhead

Node.js maintains 100 percent compatibility with npm packages. Bun works with approximately 97 percent of npm packages, while Deno manages about 85 percent using the npm: specifier. This 3 percent gap in Bun can stall migrations for weeks if a service relies on obscure Node.js internals. Deno 2 increases this compatibility by allowing users to import npm modules via URLs. Ryan Dahl stated that Deno 2 provides the ability to run complex frameworks like Next.js out of the box. Deno 2 also supports npm workspaces and allows developers to add dependencies using the deno add subcommand. Deno 2 introduces the deno install command with an –entrypoint flag to install all dependencies from a specific module. Deno 2 also includes a deno remove subcommand and a concise lockfile format, version 4, to minimize diffs during dependency updates. TypeScript handling differs across the three runtimes. Bun and Deno provide native, zero-config TypeScript support. Developers using Node.js face a burden managing tsconfig.json files. All three runtimes include native test runners, but Bun’s Jest-compatible API is more ergonomic than the Node.js runner added in version 18. Deno also supports a form of npm workspaces to help developers manage interdependent packages in one repository. Ryan Dahl expects that in five years, Chrome will execute TypeScript natively by performing type-stripping inside the V8 engine.

Deno production stability and the Cloudflare transition

Deno is ready for production use cases because it provides long-term support and API stability. The Deno team joined Cloudflare on October 9, 2026. Deno Deploy shuts down in approximately six months, and the Deno runtime receives one year of maintenance before development ends. This timeline forces teams to plan migrations away from Deno Deploy. A developer migrating a Fresh 2 SSR site from Deno Deploy to Cloudflare Workers found that the application code only required two Deno-specific API calls to become portable because the built server exported the fetch module. The site used a 15-line worker to handle 301s for legacy /posts/* URLs, while everything else deferred to static assets. This approach removed the need for a runtime server entirely. Deno 2 simplifies permission management by changing the Deno.errors.Notcapable error to replace Deno.errors.PermissionDenied. This change helps developers distinguish between OS-level errors and runtime permissions. The permissions check for the Deno.mainModule API and the process.argv API no longer requires full –allow-read permission. Deno also allows permissions for reading and writing files that contain commas in the filename. Deno uses Rust for native bindings, which introduces some overhead for permission checks. Deno’s embrace of web standards means code written for Deno often runs unchanged in browsers and edge runtimes. Is the Deno runtime the best choice for enterprise stability given the Cloudflare acquisition?