Deno 2.5 release and the runtime competition

Deno version 2.5 delivers Permission Sets through the deno.json configuration file to provide developers with granular control over runtime permissions. Developers apply these predefined permissions at runtime using the new permission-set flag. The release includes four new testing API hooks: Deno.test.beforeAll, Deno.test.beforeEach, Deno.test.afterAll, and Deno.test.afterEach. These hooks give test authors lifecycle control directly in Deno.test. Deno 2.5 upgrades the runtime to V8 14.0 and TypeScript 5.9.2 to allow access to newer JavaScript features and improved TypeScript support. The update also modifies the Temporal API for date and time management to make the –unstable-temporal flag unnecessary. Memory usage in CommonJS module wrappers is lower in this version to improve interoperability with Node.js. Additionally, the emit cache persists between updates unless the underlying deno_ast version changes. Core APIs like structuredClone use a faster internal implementation, and both Buffer.subarray and Buffer.prototype.utf8Slice are optimized for binary data handling. Deno also improves WebSocket headers to allow custom headers when initiating a new connection for authentication or passing metadata. Deno’s Node-API layer received performance tuning to minimize overhead when loading native Node modules.

Comparative Performance and Security Models

Performance metrics from 2026 show wide variances between the available runtimes. Bun 1.4.2 delivers a 4x advantage in raw HTTP throughput in synthetic tests, as it handles 52,000 requests per second compared to the 13,000 requests per second produced by the current Node.js 26.7.0 release line. In real-world applications containing databases and middleware, this throughput gap narrows to 12,400 requests per second for Bun and 12,000 requests per second for Node.js. Bun 1.4.2 shows cold starts between 6 and 10 milliseconds, which makes it 4 to 10 times faster than the 50 milliseconds observed in Node.js 22. Deno 2.9.6 uses the V8 engine like Node.js but uses a Rust and Tokio core with a secure-by-default permission model. Deno requires explicit flags like –allow-net or –allow-read to access the network or file system. While Bun transpiles TypeScript files without full static type checking, Deno 2.9.6 includes an optional full type-checking pass built into its CLI. Bun 1.4.2 utilizes a 4-tier JIT compilation and uses Zig to improve speed.

Serverless Deployment and TypeScript Strategy

Serverless deployment decisions depend on the priority of cold starts or security. Deno shows faster cold start times than Bun and Node.js when running in AWS Lambda via Docker. In Hono framework tests on AWS Lambda, Deno’s cold start was 71% faster than Bun and 77% faster than Node.js. In VM environments, Deno’s cold start time is 33% faster than Bun and 36% faster than Node.js. Bun 1.4.2 provides a single binary that includes a package manager, test runner, and bundler. Bun’s package manager installs dependencies 20 to 40 times faster than npm or yarn because it uses a global cache and a binary lockfile. Deno 2.9.6 uses the npm: specifier to bridge the gap with the npm ecosystem, which covers 85% to 90% of existing packages. Node.js 26.7.0 maintains the largest ecosystem with over 2 million packages. Deno’s native TypeScript support handles enums and namespaces without the configuration required by Node.js. You should consider how much your team relies on specific native Node.js addons before switching to Deno. Bun 1.4.2 is optimized for high-throughput APIs and edge deployment. Can teams successfully migrate to Bun without encountering native module issues?