Skip to main content
Extension.js treats Deno as a first-class runtime. Scaffold with Deno and the project gets a deno.jsonc instead of a package.json. Work in a hybrid project and deno.jsonc sits beside package.json for Deno-native settings. Either way, extension dev and extension build behave the same.

​
Create a project with Deno

Then run the dev task:

​
Primary mode: deno.jsonc is the project manifest

When you scaffold under the Deno runtime, deno.jsonc becomes the project’s only manifest and package.json is removed.
  • Template dependencies move into imports as npm: specifiers, and deno install resolves them.
  • The extension engine itself is declared there too, as npm:extension@<version>.
  • nodeModulesDir is set to "auto", so npm: dependencies materialize in a real node_modules directory. The bundler resolves project dependencies from it at dev and build time.
  • deno task <name> also finds binaries in node_modules/.bin, so the generated tasks run the locally installed Extension.js CLI.
A trimmed example:
When a template ships its own Deno config, Extension.js merges into that file instead of creating a second one. Deno’s own discovery prefers deno.json over deno.jsonc, so the merge targets the file that Deno will read.

​
Companion mode: deno.jsonc beside package.json

Monorepo templates, and projects that already have a package.json, keep it. Dependencies stay declared in package.json, and deno install resolves them from there. The companion deno.jsonc carries only Deno-native settings and the tasks that run the CLI.

​
How the toolchain detects Deno

Detection works on files, not on how you invoked the CLI:
  • Extension.js reads deno.jsonc or deno.json when it scans project dependencies. Framework, CSS, and TypeScript detection all see packages that imports declares through npm: specifiers.
  • When both manifests declare the same package, the package.json entry wins.
  • A project counts as Deno-managed when it has a deno.lock, or a Deno config with no package.json beside it. An npm-family lockfile wins for hybrids, and Deno is claimed only when the deno binary is on your PATH.

​
TypeScript in Deno projects

TypeScript detection follows the same rules as everywhere else. See TypeScript: SWC compiles the sources, and the typescript package is only needed for tsc --noEmit.

​
Next steps