Using packages

You can use JSR packages in any runtime that supports ES modules, like Deno, Node.js, Bun, Cloudflare Workers, etc. You can also use JSR packages with bundlers that support ES modules, such as Vite, esbuild, Webpack, and Rollup.

Adding a package

You can add a JSR package to your project using any of the commands below - the example below will add the most recent version of @luca/cases to your project.

# deno
deno add jsr:@luca/cases

# npm (one of the below, depending on your package manager)
npx jsr add @luca/cases
yarn dlx jsr add @luca/cases
pnpm dlx jsr add @luca/cases
bunx jsr add @luca/cases

If you’re using Deno, the deno add command will add an import map entry for the JSR module you specified in a deno.json file. That entry will look something like this:

{
  "imports": {
    "@luca/cases": "jsr:@luca/cases@^1.0.1"
  }
}

For npm and npm-compatible package managers, the jsr command will add the dependency to your package.json file, along with a .npmrc file to your project root with the necessary config to use JSR with npm. Learn more about JSR’s npm compatibility layer.

After installation with npx jsr add, your package.json will contain a dependency entry that looks something like this:

{
  "dependencies": {
    "@luca/cases": "npm:@jsr/luca__cases@^1.0.1"
  }
}

This npm dependency configuration makes use of a special custom scope called @jsr, which is now configured for you in .npmrc:

@jsr:registry=https://npm.jsr.io

NOTE: You should check the new .npmrc file into source control - it will be needed to install updates to JSR modules.

Once your package has been added, you can use it in your ES module code the same way across runtimes:

import { camelCase } from "@luca/cases";

camelCase("hello world"); // "helloWorld"

Importing with jsr: specifiers

In Deno, you can use packages without an install step by using jsr: specifiers directly within your source files. In this example, we import the @luca/cases module directly in our code, without needing an import map entry.

import { camelCase } from "jsr:@luca/cases@^1.0.1";

camelCase("hello world"); // "helloWorld"

Here the jsr: specifier is followed by the package scope, the package name, a semver constraint, and optionally an entrypoint.

Semver resolution

JSR uses semantic versioning to resolve package versions. This means that you can use a semver range in your jsr: specifier, import map, or package.json "dependencies" entry, and then the runtime or package manager will download the latest version that satisfies all constraints for the package.

If you only care about the major version, you can specify just the major version:

# deno
deno add jsr:@luca/cases@1

# npm (and npm-like systems)
npx jsr add @luca/cases@1

If you want to use a specific minor version, you can specify the minor version:

# deno
deno add jsr:@luca/[email protected]

# npm (and npm-like systems)
npx jsr add @luca/[email protected]

If you want to use a specific patch version, you can specify the patch version:

# deno
deno add jsr:@luca/[email protected]

# npm (and npm-like systems)
npx jsr add @luca/[email protected]

If you want to use at least a specific patch version, but do want to allow
updates, you can specify the patch version with a ^ prefix:

# deno
deno add jsr:@luca/cases@^1.0.1

# npm (and npm-like systems)
npx jsr add @luca/cases@^1.0.1

Learn more about semantic versioning here.

Entrypoints

Every package on JSR has one or more entrypoints. An entrypoint is a module that can be imported by users of the package. The entrypoint is specified in the exports field of the package’s config file. Learn more about exports.

If you don’t specify an entrypoint in your import, the runtime will use the package’s default entrypoint. For example, when you import jsr:@luca/cases@1, you import the default entrypoint of the @luca/cases package.

You can also import other entrypoints from a package. To do this, specify the entrypoint after the version constraint:

import { join } from "jsr:@std/path@1/join";

If you’re using an import map, or a package.json, you can specify the entrypoint after the alias:

import { join } from "@std/path/join";

Files not listed in the exports field are not directly importable by users of the package. However, they can be imported by other modules in the package.

Packages are not required to have a default entrypoint. If a package does not have a default entrypoint, then you must specify an entrypoint in your import.