esm-compiler

library0.9.2jsnpmunverified

ESM Compiler is a Rust-based compiler for the esm.sh playground, leveraging swc for JavaScript/TypeScript/JSX transformation and lightningcss for CSS. Built as a WebAssembly module, it compiles modern frontend code into ESM-compatible output with import maps. Version 0.9.2 is the current stable release; it is actively developed as part of the esm.sh ecosystem. Key differentiators include its Wasm-first architecture, Rust performance, and tight integration with esm.sh's import map resolution, making it suitable for in-browser code transformation without a server.

web-framework

npm install esm-compiler

github ↗package ↗homepage ↗

INSTALL

IMPORT

SIG · ESM-COMPILER

esm-compiler

web-frameworkjavascriptv0.9.2

harness data pending

Install & Compatibility

Where this runs

No compatibility data collected yet for this library.

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

init

✓ import init, { transform } from 'https://esm.sh/esm-compiler'

✗ const init = require('esm-compiler')

This is an ESM package loaded via URL (esm.sh). init() must be called to load the Wasm module before using transform.

transform

✓ import { transform } from 'https://esm.sh/esm-compiler'

✗ import transform from 'esm-compiler'

transform is a named export, not default. Must be destructured from the module.

TransformOptions

✓ import type { TransformOptions } from 'https://esm.sh/esm-compiler'

✗ import { TransformOptions } from 'esm-compiler'

TransformOptions is a TypeScript type and should be imported using import type for runtime efficiency in bundlers.

Initializes the Wasm compiler, transforms a React JSX component with an import map, and logs the compiled ESM output.

import init, { transform } from 'https://esm.sh/esm-compiler@0.9.2'; await init(); const code = ` import { useState } from "react"; export default function App() { const [msg] = useState("world"); return <h1>Hello {msg}!</h1>; } `; const importMap = { imports: { "@jsxImportSource": "https://esm.sh/react@18", "react": "https://esm.sh/react@18" } }; const result = transform('./App.tsx', code, { importMap }); console.log(result.code);

Debug

Known issues

breakinginit() must be called before any transform call

fix

Ensure init() is awaited once at the start of your application.

affects: all

breakingVersion 0.9.x changed import resolution to require full URL imports

fix

Use the full esm.sh URL (https://esm.sh/esm-compiler) instead of a local or npm import.

affects: >=0.9.0

deprecatedThe previous synchronous transform API is deprecated

fix

Use the async transform function returned after init().

affects: >=0.9.0

gotchaTypeScript types are only exported as type-only; cannot be used as runtime values

fix

Use 'import type { ... }' for type imports to avoid bundling errors.

affects: all

gotchaimportMap.imports must include '@jsxImportSource' for JSX to work correctly

fix

Always specify the JSX import source in the import map imports object.

affects: all

Errors

Common errors & fixes

Error: transform is not a function

init() was not called or the Wasm module failed to load

fix

Call await init() before calling transform, and check network requests for the .wasm file.

Uncaught (in promise) TypeError: Cannot read properties of undefined (reading '__wbg_...')

Calling transform before init() has completed

fix

Wrap your transform calls in an async function and ensure init() is awaited.

Module parse failed: Unexpected token (10:20) You may need an appropriate loader to handle this file type.

Bundler (e.g., webpack) cannot handle Wasm blob URL or ES module imports from esm.sh

fix

Use a bundler like Vite or configure webpack to support WebAssembly and esm.sh imports.

Upgrade

Version history

0.9.2latest on npm

Audit

Dependencies

swcrequiredJavaScript/TypeScript/JSX transformation engine

lightningcssrequiredCSS minification and transformation

Agent activity

2 hits · last 30 days

node

Resources

githubhttps://github.com/esm-dev/esm-compiler ↗

packagehttps://www.npmjs.com/package/esm-compiler ↗

homepagehttps://esm.sh ↗