esmod

library1.0.0jsnpmunverified

esmod is a fast in-place transpiler for converting ES6 import/export statements to CommonJS require/exports. Version 1.0.0 is currently stable, with a focus on speed by leveraging AST-based transformation rather than regex-only approaches. It distinguishes itself from tools like esbuild or Babel by being designed for lightweight, single-file transformations without module resolution or bundling — ideal for build tool authors and custom pipelines.

serialization

npm install esmod

github ↗package ↗

INSTALL

IMPORT

SIG · ESMOD

esmod

serializationjavascriptv1.0.0

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.

transform

✓ import { transform } from 'esmod'

✗ const transform = require('esmod').transform

ESM-only package; CommonJS require() does not work natively unless in a Node ESM context.

transformSync

✓ import { transformSync } from 'esmod'

✗ import transformSync from 'esmod'

transformSync is a named export, not a default export.

default transform

✓ import transform from 'esmod'

✗ const { transform } = require('esmod')

The default export is a shorthand for the transform function.

Converts an ES module file (.mjs) to CommonJS (.cjs) using esmod's transform function with explicit source and target formats.

import { transform } from 'esmod'; import { readFileSync, writeFileSync } from 'fs'; const code = readFileSync('input.mjs', 'utf8'); const result = transform(code, { from: 'esm', to: 'cjs' }); writeFileSync('output.cjs', result.code); console.log('Transformed successfully!');

esmod --version

Debug

Known issues

gotchatransform() throws synchronous errors; do not use try/catch with async error patterns.

fix

Wrap in try/catch (not .catch()) since it's not a Promise.

affects: >=1.0.0

gotchaInput code must contain only valid ES module syntax; mixing require() and import will cause parse errors.

fix

Ensure code is pure ES module syntax before passing to transform.

affects: >=1.0.0

deprecatedoptions.from and options.to are optional; default is ESM-to-ESM (no-op), which may be unexpected.

fix

Always specify both targets to avoid accidental no-op.

affects: >=1.0.0

Errors

Common errors & fixes

TypeError: Cannot read properties of undefined (reading 'code')

Calling transform() without waiting for a Promise, but it's actually synchronous and returns an object directly.

fix

Access result.code immediately after calling transform() without await.

SyntaxError: Unexpected token 'export'

Input contains export statements but options.from is not set to 'esm', so transform treats input as CommonJS.

fix

Set { from: 'esm' } in options.

Error: No transform applied because source and target are the same.

Both from and to options are set to 'esm', resulting in no transformation.

fix

Set 'to' to 'cjs' to convert to CommonJS.

Upgrade

Version history

1.0.0latest on npm

Audit

Dependencies

No dependency data recorded yet.

Agent activity

4 hits · last 30 days

node

Resources

githubhttps://github.com/rreverser/esmod ↗

packagehttps://www.npmjs.com/package/esmod ↗