Deno vs Bun: Which Modern JS Runtime for CI?
Both are all-in-one Node alternatives, but Deno leans on security and standards while Bun chases raw speed and drop-in Node compatibility.
Deno is a secure-by-default runtime with built-in TypeScript, tooling, and an explicit permissions model. Bun is a JavaScriptCore-based runtime focused on speed, bundling its own installer, test runner, and bundler with strong Node compatibility.
| Deno | Bun | |
|---|---|---|
| Focus | Security + standards | Speed + Node compatibility |
| Built-in tooling | Fmt, lint, test, bundle | Install, test, bundle |
| Permissions model | Opt-in sandbox | Full access (like Node) |
| Node compatibility | Good, improving | High |
| Install speed | Fast | Very fast |
In CI
Bun tends to be the fastest for installs and test runs and is the easier drop-in for existing Node projects. Deno offers a stricter security model and standards-first design, which appeals when you want explicit, auditable CI permissions. Both bundle tooling that removes separate install steps, but each can hit edge cases with native or Node-specific packages.
Speed it up
Cache the dependency cache keyed on your lockfile on either runtime. Both run the same on CI runners; faster managed runners shorten heavy install, test, and bundle steps.
The verdict
Want the fastest, most Node-compatible all-in-one toolkit: Bun. Want a security-first, standards-driven runtime with built-in tooling: Deno. Validate your dependency tree on whichever you choose before committing CI.