ESM

A fast, global content delivery network to transform NPM packges to standard ES Modules by esbuild.

Import from URL

import React from 'https://esm.sh/react'

Specify version

import React from 'https://esm.sh/react@17.0.2'

or use a major version:

import React from 'https://esm.sh/react@17'

Submodule

import { renderToString } from 'https://esm.sh/react-dom/server'

or import non-module(js) files:

import 'https://esm.sh/tailwindcss/dist/tailwind.min.css'

Bundle mode

import { Button } from 'https://esm.sh/antd?bundle'

In bundle mode, all dependencies will be bundled into one JS file.

Development mode

import React from 'https://esm.sh/react?dev'

The ?dev mode builds code with NODE_ENV equals to development, that is useful to build modules like React to allow you get more development warn/error messages.

Specify external dependencies

import React from 'https://esm.sh/react@16.14.0'
import useSWR from 'https://esm.sh/swr?deps=react@16.14.0'

By default, esm.sh rewrites import specifier based on the package’s dependency statement. To specify version of dependencies you can use the ?deps=PACKAGE@VERSION query, separate multiple dependencies with commas: ?deps=react@16.14.0,react-dom@16.14.0.

Aliasing dependencies

import useSWR from 'https://esm.sh/swr?alias=react:preact/compat'

in combination with ?deps:

import useSWR from 'https://esm.sh/swr?alias=react:preact/compat&deps=preact@10.5.14'

The origin idea was came from @lucacasonato.

Specify ESM target

import React from 'https://esm.sh/react?target=es2020'

By default, esm.sh will check the User-Agent header to get the build target automatically. You can specify it with the ?target query. Available targets: es2015 - es2021, esnext, node, and deno.

Package CSS

import Daygrid from 'https://esm.sh/@fullcalendar/daygrid'

<link rel="stylesheet" href="https://esm.sh/@fullcalendar/daygrid?css">

This only works when the NPM module imports css files in JS directly.

Deno compatibility

esm.sh will resolve the node internal modules (fs, os, etc.) with deno.land/std/node to support some packages working in Deno, like postcss:

import postcss from 'https://esm.sh/postcss'
import autoprefixer from 'https://esm.sh/autoprefixer'

const { css } = await postcss([ autoprefixer ]).process(`
  backdrop-filter: blur(5px);
  user-select: none;
`).async() 
console.log(css)

X-Typescript-Types

By default, esm.sh will respond with a custom X-TypeScript-Types HTTP header when types (.d.ts) are defined. This is useful for deno type checks (link).

figure #1

You can pass the no-check query to disable the X-TypeScript-Types header if some types are incorrect:

import unescape from 'https://esm.sh/lodash/unescape?no-check'

Network of esm.sh

Main server in HK
Global CDN by Cloudflare
China CDN by Aliyun (use mmdb_china_ip_list to split traffic)

Self-Hosting

You will need Go 1.16+ to compile the server, and ensure supervisor installed on your host machine.
The server runtime will install the nodejs (14 LTS) automatically.

$ git clone https://github.com/postui/esm.sh
$ cd esm.sh
$ sh ./scripts/deploy.sh

Deploying with Docker: An example Dockerfile is found in the root of this project.