undici-shim

A small ESM/UMD library providing the fast request function from Undici within Node, otherwise window.fetch is utilized when running in a browser environment.

Why?

Upon trying to distribute a project, I found Undici could not be used on the client-side.
As such, this is a drop-in replacement for Undici when using bundlers like webpack/rollup.

Without the overhead of WHATWG Streams, the request method proves much faster than fetch in both latency and throughput.

Tests	Samples	Results	Tolerance	Difference with slowest
undici - fetch	20	1028.31 req/sec	± 2.71 %	-
http - no keepalive	10	3891.51 req/sec	± 2.00 %	+ 278.44 %
undici - pipeline	95	6034.47 req/sec	± 2.95 %	+ 486.83 %
http - keepalive	50	6382.57 req/sec	± 2.98 %	+ 520.68 %
undici - request	15	8528.35 req/sec	± 2.11 %	+ 729.35 %

Install

Bun (Recommended) - bun add undici-shim
PNPM - pnpm i undici-shim

Usage

ESM

When importing, the request method is used by default, though it also works as a named export.

import request from 'undici-shim'
// or
import { request } from 'undici-shim'

Then simply call it asynchronously and return the response as usual. However, methods like .json() and .text() have been moved to the body instead of the response like the standard fetch.

const res = await request('https://jsonplaceholder.typicode.com/posts/1')
console.log(await res.body.json())

For consistency across environments, you can use Undici fetch instead.

import { fetch } from 'undici-shim'

const res = await fetch('https://jsonplaceholder.typicode.com/posts/1')
console.log(await res.json())

CommonJS

const { fetch } = require('undici-shim')

fetch('https://jsonplaceholder.typicode.com/posts/1')
    .then(res => res.json())
    .then(console.log)

Named Exports

Node
Starting from v1.3.2, named exports are identical to Undici.

import { request, Dispatcher, Headers, ... } = from 'undici-shim'

Browser

import { fetch, Request, Response, Headers } = from 'undici-shim'