created_at2022-07-14 17:18:41.693956
updated_at2023-07-19 05:43:07.159944
description[SWC plugin] workaround for jest



[SWC plugin] workaround for jest npm

Test with @swc/core@latest

This is a SWC plugin to handle jest compatibility issues.

This SWC plugin should be used with @swc/jest.

plugin version



npm i -D jest @swc/core @swc/jest jest_workaround
// jest.config.js
const fs = require("node:fs");

const swcrc = JSON.parse(fs.readFileSync(".swcrc", "utf8"));

// If you have other plugins, change this line.
((swcrc.jsc ??= {}).experimental ??= {}).plugins = [["jest_workaround", {}]];

module.exports = {
  transform: {
    "^.+\\.(t|j)sx?$": ["@swc/jest", swcrc],

Make sure that module.type is commonjs in your .swcrc since this plugin does not touch non-workaround parts, such as import statements.


1. When do I need this?

If you're using the swc compiler to transform your code to comply with the ESM specification, but you're also using Jest to test it in a CJS environment, you may encounter issues due to the immutable issue of exports.

This plugin can help by transforming the export statements into mutable exports.

2. Do I have a better choice?

You may have other options depending on your specific needs:

  • If you're able to run Jest in an ESM environment, you can use swc to transpile TypeScript/JSX syntax or downgrade JavaScript syntax without module conversion. Simply set the value of module.type to es6 to achieve this.

  • It's possible that some issues related to running Jest in an ESM environment will be resolved over time. Keep an eye on facebook/jest#9430 for updates.

  • If you don't need the behavior of ESM specifically, you can stick with the CJS syntax to get the CJS behavior of exports.

These options may be worth considering before using this plugin.

CJS syntax = function foo() {
  return 42;

CTS(CJS in TypeScript) syntax

export = {
  foo: function foo() {
    return 42;


  • ESM style export means immutable exports when transformed into CJS
  • ESM style import means hoisted require when transformed into CJS

3. After upgrading the plugin version, the changes have not taken effect.

This is a known issue. You could remove the Jest cache by running jest --clearCache as a workaround.

Commit count: 108

cargo fmt