deno

Deno

A JavaScript and TypeScript runtime with a package manager, formatter, linter, test runner, type checker, and bundler in one binary. Runs TypeScript directly.

Needs Deno 2.9+. Check with deno --version, update with deno upgrade.

Deno works the way npm and bun do

Deno is not a separate ecosystem to port code into:

• deno install reads an existing package.json and writes a real node_modules.
• deno add express installs from npm. Unprefixed names default to npm.
• deno task build runs scripts.build from package.json or tasks.build from deno.json. If both define it, deno.json wins.
• Node built-ins work prefixed or not: node:fs and fs both resolve.
• deno main.js runs a file. deno run is optional.
• Deno reads tsconfig.json.

Don't tell users to rewrite imports, adopt JSR, or restructure as a precondition. The two real differences are permissions and npm lifecycle scripts not running by default.

Single-file scripts need no build step and no tsconfig.json. Applications and framework projects keep their normal setup.

To convert an existing project, see the migrate-to-deno skill.

Dependency management

deno install                  # install everything declared
deno add express              # from npm (unprefixed = npm)
deno add jsr:@std/path        # from JSR
deno add -D vitest            # dev dependency (package.json only)
deno remove express
deno outdated                 # list outdated deps
deno update                   # alias for `deno outdated --update`
deno update --latest          # ignore existing semver ranges
deno list                     # declared deps + resolved versions (npm ls)
deno why express              # why a package is in the tree
deno audit                    # vulnerability audit
deno ci                       # clean reproducible install for CI
dx cowsay hello               # run a package binary without installing (npx)

deno ci is the CI command, not deno install: it requires deno.lock, deletes node_modules, installs strictly from the lockfile, and fails if the lockfile is stale. --prod skips devDependencies.