Node and npm Compatibility

• Deno is Node-compatible. Most Node projects will run in Deno with little or no change!
• Deno supports npm packages. Just use the npm: specifier in the import, and Deno takes care of the rest.

For example, here's how you'd import Hono from npm in a Deno project:

import { Hono } from "npm:hono";

That's all you really need to know to get started! However, there are some key differences between the two runtimes that you can take advantage of to make your code simpler and smaller when migrating your Node.js projects to Deno.

Quick start Jump to heading#

Import an npm package Jump to heading#

import chalk from "npm:chalk@5";
console.log(chalk.green("Hello from npm in Deno"));

deno run main.ts

Execute CommonJS Jump to heading#

Use .cjs extension to inform Deno that module is using CommonJS system.

const chalk = require("chalk");
console.log(chalk.green("Hello from npm in Deno"));

deno run main.cjs

Use a Node API Jump to heading#

import path from "node:path";
console.log(path.join("./foo", "../bar"));

Using Node's built-in modules Jump to heading#

Deno provides a compatibility layer that allows the use of Node.js built-in APIs within Deno programs. However, in order to use them, you will need to add the node: specifier to any import statements that use them:

import * as os from "node:os";
console.log(os.cpus());

And run it with deno run main.mjs - you will notice you get the same output as running the program in Node.js.

Updating any imports in your application to use node: specifiers should enable any code using Node built-ins to function as it did in Node.js.

To make updating existing code easier, Deno will provide helpful hints for imports that don't use node: prefix:

import * as os from "os";
console.log(os.cpus());

$ deno run main.mjs
error: Relative import path "os" not prefixed with / or ./ or ../
  hint: If you want to use a built-in Node module, add a "node:" prefix (ex. "node:os").
    at file:///main.mjs:1:21

The same hints and additional quick-fixes are provided by the Deno LSP in your editor.

Explore built-in Node APIs

Using npm packages Jump to heading#

Deno has native support for importing npm packages by using npm: specifiers. For example:

import * as emoji from "npm:node-emoji";

console.log(emoji.emojify(`:sauropod: :heart:  npm`));

Can be run with:

$ deno run main.js
🦕 ❤️ npm

No npm install is necessary before the deno run command and no node_modules folder is created. These packages are also subject to the same permissions as other code in Deno.

First-class package.json support Jump to heading#

Deno understands package.json in your project. You can:

• Declare dependencies there (alongside or instead of inline npm: specifiers).
• Use scripts from package.json via deno task (for example, deno task start).
• Rely on package.json fields like type when resolving modules (see CommonJS support below).

By default, dependencies are stored in Deno's global cache without creating a local node_modules directory. If your tools expect node_modules, opt-in using nodeModulesDir in deno.json.

npm specifiers have the following format:

npm:[@][/]

This also allows functionality that may be familar from the npx command.

# npx allows remote execution of a package from npm or a URL
$ npx create-next-app@latest

# deno run allows remote execution of a package from various locations,
# and can scoped to npm via the `npm:` specifier.
$ deno run -A npm:create-next-app@latest

For examples with popular libraries, please refer to the tutorial section.

Node.js global objects Jump to heading#

In Node.js, there are a number of global objects available in the scope of all programs that are specific to Node.js, eg. process object.

Here are a few globals that you might encounter in the wild and how to use them in Deno:

• process - Deno provides the process global, which is by far the most popular global used in popular npm packages. It is available to all code. However, Deno will guide you towards importing it explicitly from node:process module by providing lint warnings and quick-fixes:

console.log(process.versions.deno);

$ deno run process.js
2.0.0
$ deno lint process.js
error[no-process-global]: NodeJS process global is discouraged in Deno
 --> /process.js:1:13
  |
1 | console.log(process.versions.deno);
  |             ^^^^^^^
  = hint: Add `import process from "node:process";`

  docs: https://docs.deno.com/lint/rules/no-process-global


Found 1 problem (1 fixable via --fix)
Checked 1 file

• require() - see CommonJS support

• Buffer - to use Buffer API it needs to be explicitly imported from the node:buffer module:

import { Buffer } from "node:buffer";

const buf = new Buffer(5, "0");

For TypeScript users needing Node.js-specific types like BufferEncoding, these are available through the NodeJS namespace when using @types/node:

/// <reference types="npm:@types/node" />

// Now you can use NodeJS namespace types
function writeToBuffer(data: string, encoding: NodeJS.BufferEncoding): Buffer {
  return Buffer.from(data, encoding);
}

Prefer using Uint8Array or other TypedArray subclasses instead.

• __filename - use import.meta.filename instead.

• __dirname - use import.meta.dirname instead.

CommonJS support Jump to heading#

Deno supports CommonJS modules by default.

Note: Deno's permission system still applies to CommonJS code. You may need --allow-read because Deno probes package.json and node_modules to resolve CommonJS modules.

Use .cjs extension Jump to heading#

If the file extension is .cjs Deno will treat this module as CommonJS.

const express = require("express");

Deno does not look for package.json files and type option to determine if the file is CommonJS or ESM.

When using CommonJS, Deno expects that dependencies will be installed manually and a node_modules directory will be present. It's best to set "nodeModulesDir": "auto" in your deno.json to ensure that.

$ cat deno.json
{
  "nodeModulesDir": "auto"
}

$ deno install npm:express
Add npm:express@5.0.0

$ deno run -R -E main.cjs
[Function: createApplication] {
  application: {
    init: [Function: init],
    defaultConfiguration: [Function: defaultConfiguration],
    ...
  }
}

-R and -E flags are used to allow permissions to read files and environment variables.

You can also just run a .cjs file directly:

deno run -A main.cjs

package.json type option Jump to heading#

Deno will attempt to load .js, .jsx, .ts, and .tsx files as CommonJS if there's a package.json file with "type": "commonjs" option next to the file, or up in the directory tree when in a project with a package.json file.

{
  "type": "commonjs"
}

const express = require("express");

Tools like Next.js's bundler and others will generate a package.json file like that automatically.

If you have an existing project that uses CommonJS modules, you can make it work with both Node.js and Deno, by adding "type": "commonjs" option to the package.json file.

Always detecting if a file might be CommonJS Jump to heading#

Telling Deno to analyze modules as possibly being CommonJS is possible by running with the --unstable-detect-cjs in Deno >= 2.1.2. This will take effect, except when there's a package.json file with { "type": "module" }.

Looking for package.json files on the file system and analyzing a module to detect if its CommonJS takes longer than not doing it. For this reason and to discourage the use of CommonJS, Deno does not do this behavior by default.

Create require() manually Jump to heading#

An alternative option is to create an instance of the require() function manually:

import { createRequire } from "node:module";
const require = createRequire(import.meta.url);
const express = require("express");

In this scenario the same requirements apply, as when running .cjs files - dependencies need to be installed manually and appropriate permission flags given.

require(ESM) Jump to heading#

Deno's require() implementation supports requiring ES modules.

This works the same as in Node.js, where you can only require() ES modules that don't have Top-Level Await in their module graph - or in other words you can only require() ES modules that are "synchronous".

export function greet(name) {
  return `Hello ${name}`;
}

import { greet } from "./greet.js";

export { greet };

const esm = require("./esm");
console.log(esm);
console.log(esm.greet("Deno"));

$ deno run -R main.cjs
[Module: null prototype] { greet: [Function: greet] }
Hello Deno

Import CommonJS modules Jump to heading#

You can also import CommonJS files in ES modules.

module.exports = {
  hello: "world",
};

import greet from "./greet.js";
console.log(greet);

$ deno run main.js
{
  "hello": "world"
}

Hints and suggestions Jump to heading#

Deno will guide you when a file looks like CommonJS but isn’t loaded as such. If you see an error about module not being defined, fix it by one of the following:

• Rewrite to ESM
• Change the file extension to .cjs
• Add a nearby package.json with { "type": "commonjs" }
• Run with --unstable-detect-cjs

See docs: CommonJS in Deno

Conditional exports Jump to heading#

Package exports can be conditioned on the resolution mode. The conditions satisfied by an import from a Deno ESM module are as follows:

["deno", "node", "import", "default"]

This means that the first condition listed in a package export whose key equals any of these strings will be matched. You can expand this list using the --unstable-node-conditions CLI flag:

deno run --unstable-node-conditions development,react-server main.ts

["development", "react-server", "deno", "node", "import", "default"]

Importing types Jump to heading#

Many npm packages ship with types, you can import these and use them with types directly:

import chalk from "npm:chalk@5";

Some packages do not ship with types but you can specify their types with the @ts-types directive. For example, using a @types package:

// @ts-types="npm:@types/express@^4.17"
import express from "npm:express@^4.17";

Module resolution Jump to heading#

The official TypeScript compiler tsc supports different moduleResolution settings. Deno only supports the modern node16 resolution. Unfortunately many npm packages fail to correctly provide types under node16 module resolution, which can result in deno check reporting type errors, that tsc does not report.

If a default export from an npm: import appears to have a wrong type (with the right type seemingly being available under the .default property), it's most likely that the package provides wrong types under node16 module resolution for imports from ESM. You can verify this by checking if the error also occurs with tsc --module node16 and "type": "module" in package.json or by consulting the Are the types wrong? website (particularly the "node16 from ESM" row).

If you want to use a package that doesn't support TypeScript's node16 module resolution, you can:

1. Open an issue at the issue tracker of the package about the problem. (And perhaps contribute a fix :) (Although, unfortunately, there is a lack of tooling for packages to support both ESM and CJS, since default exports require different syntaxes. See also microsoft/TypeScript#54593)
2. Use a CDN, that rebuilds the packages for Deno support, instead of an npm: identifier.
3. Ignore the type errors you get in your code base with // @ts-expect-error or // @ts-ignore.

Including Node types Jump to heading#

Node ships with many built-in types like Buffer that might be referenced in an npm package's types. To load these you must add a types reference directive to the @types/node package:

/// <reference types="npm:@types/node" />

Note that it is fine to not specify a version for this in most cases because Deno will try to keep it in sync with its internal Node code, but you can always override the version used if necessary.

Run npm binaries Jump to heading#

You can run npm CLI tools (packages with bin entries) directly without npm install by using an npm: specifier:

npm:[@][/]

For example:

$ deno run --allow-read npm:cowsay@1.5.0 "Hello there!"
 ______________
< Hello there! >
 --------------
        \   ^__^
         \  (oo)\_______
            (__)\       )\/\
                ||----w |
                ||     ||

$ deno run --allow-read npm:cowsay@1.5.0/cowthink "What to eat?"
 ______________
( What to eat? )
 --------------
        o   ^__^
         o  (oo)\_______
            (__)\       )\/\
                ||----w |
                ||     ||

node_modules Jump to heading#

When you run npm install, npm creates a node_modules directory in your project which houses the dependencies as specified in the package.json file.

Deno uses npm specifiers to resolve npm packages to a central global npm cache, instead of using a node_modules folder in your projects. This is ideal since it uses less space and keeps your project directory clean.

There may however be cases where you need a local node_modules directory in your Deno project, even if you don’t have a package.json (eg. when using frameworks like Next.js or Svelte or when depending on npm packages that use Node-API).

Choosing a node_modules mode Jump to heading#

• Use no local node_modules (default) when your project runs fine with Deno's global cache. No setup required.
• Use auto when some tools expect node_modules or you rely on Node-API addons and want automatic creation.
• Use manual when your project has a package.json and you prefer an explicit install step.

Default Deno dependencies behavior Jump to heading#

By default, Deno will not create a node_modules directory when you use the deno run command, dependencies will be installed into the global cache. This is the recommended setup for new Deno projects.

Automatic node_modules creation Jump to heading#

If you need a node_modules directory in your project, you can use the --node-modules-dir flag or nodeModulesDir: auto option in the config file to tell Deno to create a node_modules directory in the current working directory:

deno run --node-modules-dir=auto main.ts

or with a configuration file:

{
  "nodeModulesDir": "auto"
}

The auto mode automatically installs dependencies into the global cache and creates a local node_modules directory in the project root. This is recommended for projects that have npm dependencies that rely on node_modules directory - mostly projects using bundlers or ones that have npm dependencies with postinstall scripts.

Manual node_modules creation Jump to heading#

If your project has a package.json file, you can use the manual mode, which requires an installation step to create your node_modules directory:

deno install
deno run --node-modules-dir=manual main.ts

or with a configuration file:

{ "nodeModulesDir": "manual" }

You would then run deno install/npm install/pnpm install or any other package manager to create the node_modules directory.

Manual mode is the default mode for projects using a package.json. You may recognize this workflow from Node.js projects. It is recommended for projects using frameworks like Next.js, Remix, Svelte, Qwik etc, or tools like Vite, Parcel or Rollup.

node_modules flag Jump to heading#

You can also enable the creation of a node_modules directory on a per-command basis with the --node-modules-dir flag.

import chalk from "npm:chalk@5";

console.log(chalk.green("Hello"));

deno run --node-modules-dir main.ts

Running the above command, with a --node-modules-dir flag, will create a node_modules folder in the current directory with a similar folder structure to npm.

Node-API addons Jump to heading#

Summary: Node-API addons work in Deno when a local node_modules/ is present and you grant --allow-ffi.

Deno supports Node-API addons used by popular npm packages like esbuild, npm:sqlite3 and npm:duckdb. You can expect packages that use public Node-APIs to work.

As of Deno 2.0, npm packages using Node-API addons are supported when a local node_modules/ directory is present. Configure "nodeModulesDir": "auto" | "manual" in deno.json or run with --node-modules-dir=auto|manual.

Like all native FFI, pass --allow-ffi to grant explicit permission. Review Security and permissions.

Migrating from Node to Deno Jump to heading#

Running your Node.js project with Deno is a straightforward process. In most cases you can expect little to no changes to be required, if your project is written using ES modules.

Main points to be aware of:

1. Use the node: specifier for built-in modules (see Using Node's built-in modules above).
2. Some Node globals like Buffer must be imported from node:buffer (see Node.js global objects).
3. require() is available in .cjs files or via createRequire (see CommonJS support).

Running scripts Jump to heading#

Deno supports running npm scripts natively with the deno task subcommand (If you're migrating from Node.js, this is similar to the npm run script command). Consider the following Node.js project with a script called start inside its package.json:

{
  "name": "my-project",
  "scripts": {
    "start": "eslint"
  }
}

You can execute this script with Deno by running:

deno task start

Optional improvements Jump to heading#

Deno ships a unified toolchain (configuration, linter, formatter, test runner) that can simplify your setup when migrating:

• Configuration: /runtime/fundamentals/configuration/
• Linter: /runtime/reference/cli/linter/
• Formatter: /runtime/reference/cli/formatter/
• Test runner: /runtime/reference/cli/test/

Private registries Jump to heading#

Deno supports private registries, which allow you to host and share your own modules. This is useful for organizations that want to keep their code private or for individuals who want to share their code with a select group of people.

What are private registries? Jump to heading#

Large organizations often host their own private npm registries to manage internal packages securely. These private registries serve as repositories where organizations can publish and store their proprietary or custom packages. Unlike public npm registries, private registries are accessible only to authorized users within the organization.

How to use private registries with Deno Jump to heading#

First, configure your .npmrc file to point to your private registry. The .npmrc file must be in the project root or $HOME directory. Add the following to your .npmrc file:

@mycompany:registry=http://mycompany.com:8111/
//mycompany.com:8111/:_auth=secretToken

Replace http://mycompany.com:8111/ with the actual URL of your private registry and secretToken with your authentication token.

Then update Your deno.json or package.json to specify the import path for your private package. For example:

{
  "imports": {
    "@mycompany/package": "npm:@mycompany/package@1.0.0"
  }
}

or if you're using a package.json:

{
  "dependencies": {
    "@mycompany/package": "1.0.0"
  }
}

Now you can import your private package in your Deno code:

import { hello } from "@mycompany/package";

console.log(hello());

and run it using the deno run command:

deno run main.ts

Node to Deno Cheatsheet Jump to heading#

¹ Type checking happens automatically, TypeScript compiler is built into the deno binary.