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esm.sh
A fast, smart, & global content delivery network (CDN) for modern(es2015+) web development.
How to Use
esm.sh is a modern CDN that allows you to import es6 modules from a URL:
import Module from "https://esm.sh/PKG@SEMVER[/PATH]";
or build a module with custom input(code):
import { esm } from "https://esm.sh/build";
const { say } = await esm`
import chalk from "chalk";
export const say = () => chalk.blue("Hi!");
`;
console.log(say()); // "Hi!"
More usage check out here.
Import from NPM
import React from "https://esm.sh/react@18.2.0";
You may also use a semver or a
dist-tag instead of a
fixed version number, or omit the version/tag entirely to use the latest
tag:
import React from "https://esm.sh/react"; // 18.2.0 (latest)
import React from "https://esm.sh/react@17"; // 17.0.2
import React from "https://esm.sh/react@canary"; // 18.3.0-canary-e1ad4aa36-20230601
Import from GitHub Repos
You can also import modules/assets from a github repo:
/gh/OWNER/REPO[@TAG]/PATH
. For example:
import tslib from "https://esm.sh/gh/microsoft/tslib@2.5.0";
or load a svg image from a github repo: https://esm.sh/gh/microsoft/fluentui-emoji/assets/Party%20popper/Color/party_popper_color.svg
Import a Submodule
import { renderToString } from "https://esm.sh/react-dom@18.2.0/server";
or import non-module(js) as following:
import "https://esm.sh/react@18.2.0/package.json" assert { type: "json" };
Specify Dependencies
By default, esm.sh rewrites import specifiers based on the package dependencies.
To specify the version of these dependencies, you can add the
?deps=PACKAGE@VERSION
query. To specify multiple dependencies, separate them
with a comma, like this: ?deps=react@17.0.2,react-dom@17.0.2
.
import React from "https://esm.sh/react@17.0.2";
import useSWR from "https://esm.sh/swr?deps=react@17.0.2";
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 coming from @lucacasonato.
Tree Shaking
By default, esm.sh exports a module with all its exported members. However, if
you want to import only a specific set of members, you can specify them by
adding a ?exports=foo,bar
query to the import statement.
import { __await, __rest } from "https://esm.sh/tslib"; // 7.3KB
import { __await, __rest } from "https://esm.sh/tslib?exports=__await,__rest"; // 489B
By using this feature, you can take advantage of tree shaking with esbuild and achieve a smaller bundle size. Note that this feature is only supported for ESM modules and not CJS modules.
Bundle Mode
import { Button } from "https://esm.sh/antd?bundle";
In bundle mode, all dependencies are bundled into a single JS file except the peer dependencies.
Development Mode
import React from "https://esm.sh/react?dev";
With the ?dev
option, esm.sh builds a module with process.env.NODE_ENV
set
to "development"
or based on the condition development
in the exports
field of package.json
. This is useful for libraries that have different
behavior in development and production. For example, React will use a different
warning message in development mode.
ESBuild Options
By default, esm.sh checks the User-Agent
header to determine the build target.
You can also specify the target
by adding ?target
, available targets are:
es2015 - es2022, esnext, deno, denonext, node and bun.
import React from "https://esm.sh/react?target=es2020";
Other supported options of esbuild:
- Conditions
import foo from "https://esm.sh/foo?conditions=custom1,custom2";
- Keep names
import foo from "https://esm.sh/foo?keep-names";
- Ignore annotations
import foo from "https://esm.sh/foo?ignore-annotations";
Web Worker
esm.sh supports ?worker
query to load the module as a web worker:
import workerFactory from "https://esm.sh/monaco-editor/esm/vs/editor/editor.worker?worker";
const worker = workerFactory();
You can pass some custom code snippet to the worker when calling the factory function:
const workerAddon = `
self.onmessage = function (e) {
console.log(e.data)
}
`;
const worker = workerFactory(workerAddon);
Package CSS
<link rel="stylesheet" href="https://esm.sh/monaco-editor?css">
This only works when the package imports CSS files in JS directly.
Importing WASM Modules
esm.sh supports importing wasm modules in JS directly, to do that, you need to
add ?module
query to the import URL:
import wasm from "https://esm.sh/@dqbd/tiktoken@1.0.3/tiktoken_bg.wasm?module";
const { exports } = WebAssembly.instantiate(wasm, imports);
Specify CJS Exports
If you get an error like ...not provide an export named...
, that means esm.sh
can not resolve CJS exports of the module correctly. You can add
?cjs-exports=foo,bar
query to specify the export names:
import {
NinetyRing,
NinetyRingWithBg,
} from "https://esm.sh/react-svg-spinners@0.3.1?cjs-exports=NinetyRing,NinetyRingWithBg";
Using Import Maps
Import Maps has been supported by
most modern browsers, Reejs and Deno natively. This allows bare import
specifiers, such as import React from "react"
, to work.
esm.sh supports ?external=foo,bar
query to specify external dependencies. With
this query, esm.sh will not rewrite the import specifiers of the specified
dependencies. For example:
{
"imports": {
"preact": "https://esm.sh/preact@10.7.2",
"preact-render-to-string": "https://esm.sh/preact-render-to-string@5.2.0?external=preact"
}
}
Alternatively, you can mark all dependencies as external by adding a *
prefix before the package name:
{
"imports": {
"preact": "https://esm.sh/preact@10.7.2",
"preact-render-to-string": "https://esm.sh/*preact-render-to-string@5.2.0",
"swr": "https://esm.sh/*swr@1.3.0",
"react": "https://esm.sh/preact@10.7.2/compat"
}
}
Import maps supports
trailing slash
that can not work with URL search params friendly. To fix this issue, esm.sh
provides a special format for import URL that allows you to use query params
with trailing slash: change the query prefix ?
to &
and put it after the
package version.
{
"imports": {
"react-dom": "https://esm.sh/react-dom@18.2.0?pin=v129&dev",
"react-dom/": "https://esm.sh/react-dom@18.2.0&pin=v129&dev/"
}
}
If you are using Deno or Reejs, you can use the CLI Script to generate and update the import maps that will resolve the external dependencies automatically.
Deno Compatibility
esm.sh is a Deno-friendly CDN that resolves Nodeâs built-in modules (such as fs, os, net, etc.), making it compatible with Deno.
import express from "https://esm.sh/express";
const app = express();
app.get("/", (req, res) => {
res.send("Hello World");
});
app.listen(3000);
Reejs Compatibility
esm.sh is a Reejs-friendly CDN. That said, Reejs officially supports and promotes esm.sh as the default CDN for importing modules.
Using deno.land/x or deno.land/std ? Reejs supports them too out of the box.
For users using deno < 1.33.2
, esm.sh uses
deno.land/std@0.177.1/node as the node
compatibility layer. You can specify a different version by adding the
?deno-std=$VER
query:
import postcss from "https://esm.sh/express?deno-std=0.128.0";
X-Typescript-Types Header
Deno supports type definitions for modules with a types
field in their
package.json
file through the X-TypeScript-Types
header. This makes it
possible to have type checking and auto-completion when using those modules in
Deno.
(link).
In case the type definitions provided by the X-TypeScript-Types
header are
incorrect, you can disable it by adding the ?no-dts
query to the module import
URL:
import unescape from "https://esm.sh/lodash/unescape?no-dts";
This will prevent the X-TypeScript-Types
header from being included in the
network request, and you can manually specify the types for the imported module.
Using CLI Script
esm.sh provides a CLI script for managing imports with import maps in Deno and Reejs. This CLI script automatically resolves dependencies and uses a pinned build version for stability.
To use the esm.sh CLI script, you first need to run the init
command in your
projectâs root directory:
# For Deno
deno run -A -r https://esm.sh init
# For Reejs
reejs x https://esm.sh init
Once youâve initialized the script, you can use the following commands to manage your imports:
For Deno:
# Adding packages
deno task esm:add react react-dom # add multiple packages
deno task esm:add react@17.0.2 # specify version
deno task esm:add react:preact/compat # using alias
# Updating packages
deno task esm:update react react-dom # update specific packages
deno task esm:update # update all packages
# Removing packages
deno task esm:remove react react-dom
For Reejs:
# Adding packages
reejs task esm:add react react-dom # add multiple packages
reejs task esm:add react@17.0.2 # specify version
reejs task esm:add react:preact/compat # using alias
# Updating packages
reejs task esm:update react react-dom # update specific packages
reejs task esm:update # update all packages
# Removing packages
reejs task esm:remove react react-dom
Building a Module with Custom Input(code)
This is an experimental API that allows you to build a module with custom input(code).
- Imports NPM/GH packages
- Supports TS/JSX syntaxes
- Bundle mulitple modules into a single JS file
import build from "https://esm.sh/build";
const ret = await build({
dependencies: {
"preact": "^10.13.2",
"preact-render-to-string": "^6.0.2",
},
code: `
/* @jsx h */
import { h } from "preact";
import { renderToString } from "preact-render-to-string";
export function render(): string {
return renderToString(<h1>Hello world!</h1>);
}
`,
// for types checking and LSP completion
types: `
export function render(): string;
`,
});
// import module
const { render } = await import(ret.url);
// import bundled module
const { render } = await import(ret.bundleUrl);
render(); // "<h1>Hello world!</h1>"
or use the esm
tag function to build and import js/ts snippet quickly in browser
with npm packages:
import { esm } from "https://esm.sh/build";
const mod = await esm`
/* @jsx h */
import { h } from "preact@10.13.2";
import { renderToString } from "preact-render-to-string@6.0.2";
export const html = renderToString(<h1>Hello world!</h1>);
`;
console.log(mod.html); // "<h1>Hello world!</h1>"
Pinning Build Version
To ensure stable and consistent behavior, you may want to pin the build version of a module youâre using from esm.sh. This helps you avoid potential breaking changes in the module caused by updates to the esm.sh server.
The ?pin
query allows you to specify a specific build version of a module,
which is an immutable cached version stored on the esm.sh CDN.
import React from "https://esm.sh/react-dom?pin=v129";
// or use version prefix
import React from "https://esm.sh/v129/react-dom";
By using the ?pin
query in the import statement, you can rest assured that the
version of the module youâre using will not change, even if updates are pushed
to the esm.sh server. This helps ensure the stability and reliability of your
application.
For UI libraries like React and Vue, esm.sh uses a special build version
stable
to ensure single version of the library is used in the whole
application.
Global CDN
The Global CDN of esm.sh is provided by Cloudflare, one of the worldâs largest and fastest cloud network platforms.
Self-Hosting
To host esm.sh by yourself, check the hosting documentation.