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1.9.0 • Public • Published


unenv is a framework-agnostic system that allows converting JavaScript code to be platform agnostic and work in any environment including Browsers, Workers, Node.js, or JavaScript runtime.


# Using npm
npm i -D unenv

# Using yarn
yarn add --dev unenv

# Using pnpm
pnpm add -D unenv


Using env utility and built-in presets, unenv will provide an abstract configuration that can be used in building pipelines (rollup.js, webpack, etc.).

import { env } from "unenv";

const { alias, inject, polyfill, external } = env({}, {}, {});

Note: You can provide as many presets as you want. unenv will merge them internally and the right-most preset has a higher priority.



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Suitable to convert universal libraries working in Node.js.

  • Add supports for global fetch API
  • Set Node.js built-ins as externals
import { env, nodeless } from "unenv";

const envConfig = env(node, {});


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Suitable to transform libraries made for Node.js to run in other JavaScript runtimes.

import { env, nodeless } from "unenv";

const envConfig = env(nodeless, {});


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This preset can be used to extend nodeless to use Deno's Node.js API Compatibility (docs, docs).

[!WARNING] This preset is experimental and behavior might change!

import { env, nodeless, deno } from "unenv";

const envConfig = env(nodeless, deno, {});


(view source)

This preset can be used to extend nodeless to use Cloudflare Worker Node.js API Compatibility (docs).

[!WARNING] This preset is experimental and behavior might change!

[!NOTE] Make sure to enable nodejs_compat compatibility flag.

import { env, nodeless, cloudflare } from "unenv";

const envConfig = env(nodeless, cloudflare, {});


This preset can be used to extend nodeless to use Vercel Edge Node.js API Compatibility (docs).

[!WARNING] This preset is experimental and behavior might change!

import { env, nodeless, vercel } from "unenv";

const envConfig = env(nodeless, vercel, {});

Built-in Node.js modules

unenv provides a replacement for all Node.js built-ins for cross-platform compatibility.

Module Status Source
node:assert Mocked -
node:async_hooks Polyfilled unenv/node/async_hooks
node:buffer Polyfilled unenv/node/buffer
node:child_process Mocked -
node:cluster Mocked -
node:console Mocked -
node:constants Mocked -
node:crypto Polyfilled unenv/node/crypto
node:dgram Mocked -
node:diagnostics_channel Mocked -
node:dns Mocked -
node:domain Mocked -
node:events Polyfilled unenv/node/events
node:fs Polyfilled unenv/node/fs
node:fs/promises Polyfilled unenv/node/fs/promises
node:http2 Mocked -
node:http Polyfilled unenv/node/http
node:https Polyfilled unenv/node/https
node:inspector Mocked -
node:module Polyfilled unenv/node/module -
node:net Polyfilled unenv/node/net
node:os Mocked -
node:path Polyfilled unenv/node/path
node:perf_hooks Mocked -
node:process Polyfilled unenv/node/process
node:punycode Mocked -
node:querystring Mocked -
node:readline Mocked -
node:repl Mocked -
node:stream Polyfilled unenv/node/stream
node:stream/consumers Mocked unenv/node/stream/consumers
node:stream/promises Mocked unenv/node/stream/promises
node:stream/web Native unenv/node/stream/web
node:string_decoder Polyfilled unenv/node/string_decoder
node:sys Mocked -
node:timers Mocked -
node:timers/promises Mocked -
node:tls Mocked -
node:trace_events Mocked -
node:tty Mocked -
node:url Polyfilled unenv/node/url
node:util Polyfilled unenv/node/util
node:util/types Polyfilled unenv/node/util/types
node:v8 Mocked -
node:vm Mocked -
node:wasi Mocked -
node:worker_threads Mocked -
node:zlib Mocked -

npm packages

unenv provides a replacement for common npm packages for cross platform compatibility.

Package Status Source
npm/consola Use native console unenv/runtime/npm/consola
npm/cross-fetch Use native fetch unenv/runtime/npm/cross-fetch
npm/debug Mocked with console.debug unenv/runtime/npm/debug
npm/fsevents Mocked unenv/runtime/npm/fsevents
npm/inherits Inlined unenv/runtime/npm/inherits
npm/mime-db Minimized unenv/runtime/npm/mime-db
npm/mime Minimized unenv/runtime/npm/mime
npm/node-fetch Use native fetch unenv/runtime/npm/node-fetch
npm/whatwg-url Use native URL unenv/runtime/npm/whatwg-url

Auto-mocking proxy

import MockProxy from "unenv/runtime/mock/proxy";


The above package doesn't work outside of Node.js and neither we need any platform-specific logic! When aliasing os to mock/proxy-cjs, it will be auto-mocked using a Proxy Object which can be recursively traversed like an Object, called like a Function, Iterated like an Array, or instantiated like a Class.

We use this proxy for auto-mocking unimplemented internals. Imagine a package does this:

const os = require("os");
if (os.platform() === "windows") {
  /* do some fix */
module.exports = () => "Hello world";

By aliasing os to unenv/runtime/mock/proxy-cjs, the code will be compatible with other platforms.

Other polyfills

To discover other polyfills, please check ./src/runtime.






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