Detect the package manager client running the current script. Detects NPM and yarn, as well as any hard executable path.

Use this when your project requires a specific package manager to work correctly, such as a monorepo using Yarn workspaces. It can help your package scripts exit early if they're being invoked outside of the required package manager.

Recommended Usage

In a monorepo, or any repo with private: true, it's safe to catch things as early as possible. Add a preinstall script to prevent the wrong package manager from even beginning to install dependencies. Use npx to dynamically install npm-is before any other modules are installed.

 {
   "name": "my-yarn-only-monorepo",
   "version": "1.0.0",
   "private": true,
   "workspaces": [
     "packages/*"
   ]
   "scripts": {
+    "preinstall": "npx npm-is yarn"
   }
 }

Now, this happens when you try to npm install.

$ npm install

> [email protected] preinstall /Users/me/repo
> npx npm-is yarn

/Users/me/repo/node_modules/npm-is/npm-is.js:54
    throw new WrongPackageManagerError(allowed, invoked);
    ^

Error: This project can only be used with the "yarn" package manager, but it was
invoked by "npm", which is not supported.

Install

Don't install this as a dependency if you're going to use it in the recommended way described above.

Instead, run it with npx so that it works before dependencies are installed!

But if you insist:

with npm: npm install --save-dev npm-is

with yarn: yarn add --dev npm-is

Advanced Usage

CLI

With no arguments, npm-is prints the current package manager. So, running it outside a package manager with no arguments, it will print nothing. Running it inside an NPM script with NPM should print npm to the command line.

With arguments, npm-is will take each of its arguments to be allowed package managers. If the preinstall script is "npm-is yarn npm", then install will only succeed if the package manager in use is Yarn or NPM. Only npm and yarn are currently supported as shorthand. If you're using a custom package manager, you must know its exec path (that is, the value of the environment variable $npm_execpath when it is running lifecycle scripts) and pass that as an argument. If the preinstall script is "npm-is /path/to/pnpm, then install will only succeed if $npm_execpath is exactly /path/to/pnpm.

Node API

const npmIs = require("npm-is");

// returns true if Yarn
npmIs("yarn");
// returns true if Yarn or NPM
npmIs(["yarn", "npm"]);
// returns true if Yarn, NPM, or custom executable
npmIs(["yarn", "npm", "/some/custom/one"]);

// Throws instead of returning false
npmIs.assert("yarn");
npmIs.assert(["yarn", "npm"]);
npmIs.assert(["yarn", "npm", "/some/custom/one"]);

// Returns "npm" if NPM, "yarn" if Yarn,
// empty string if no package manager,
// or full execPath if anything else
npmIs.detect();