deno add npm:package: add an npm or JSR dependency to a Deno project

deno add npm:express adds an npm package to a Deno project, and deno add jsr:@std/path adds a package from JSR. Deno writes the dependency to the imports map of deno.json (creating the file if needed), records the exact resolved version in deno.lock, and downloads the package, so code can then import it by its bare name: import express from "express".

Add a package

export NO_COLOR=1
npx --yes deno@2 add npm:is-odd@3 2>&1 | grep -E "^(Created|Add)"
cat deno.json
cat > main.ts <<'EOF'
import isOdd from "is-odd";
console.log(isOdd(7));
EOF
npx --yes deno@2 run main.ts

Created deno.json configuration file.
Add npm:is-odd@3.0.1
{
  "imports": {
    "is-odd": "npm:is-odd@^3.0.1"
  }
}
true

Deno resolved is-odd@3 to the newest 3.x release and stored a caret range (^3.0.1) in the import map, so later lock refreshes stay within 3.x. The example runs Deno through npx deno@2 so it needs only Node.js; with Deno installed the commands are deno add and deno run.

In a project with package.json

export NO_COLOR=1
echo '{ "name": "app", "private": true }' > package.json
npx --yes deno@2 add npm:is-odd@3.0.1 2>&1 | grep -E "^(Created|Add)"
cat package.json
ls -d node_modules

Add npm:is-odd@3.0.1
{
  "name": "app",
  "private": true,
  "dependencies": {
    "is-odd": "3.0.1"
  }
}
node_modules

When the folder has a package.json and no deno.json, Deno adds npm packages to its dependencies, like npm install, and installs them into node_modules. This keeps the project usable by Node.js tools too. With an exact version the entry is exact; with a range or no version Deno writes a caret range.

Variants

Pitfalls

• Missing prefix. Current Deno 2 releases accept a bare name (deno add is-odd was recorded as npm:is-odd), but older 2.x releases require the prefix, and a name can exist on both registries. Write npm: or jsr: to say which package you mean.
• Imports without an entry. Importing a bare name that is not in the import map fails with Import "x" not a dependency; deno add is the fix.
• Lock file conflicts. deno.lock pins the exact versions. Commit it, and run CI with --frozen-lockfile (for example deno install --frozen-lockfile) to fail when it would change.

How to confirm it worked

cat deno.json (or package.json) shows the new entry, deno.lock contains the resolved version, and deno run main.ts runs without asking for the package again. deno info main.ts prints the dependency graph of a file with the version that was used.

FAQ