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vite-plugin-cjs-interop

Vite plugin to unwrap default imports from CJS dependencies during SSR.

Problem

In Node.js, when a CJS module that contains both a default export and named exports is imported from an ESM module, the default export has to be accessed via the default property of the imported module. Prior to version 5, Vite had some logic to handle this during development, but it didn't apply to SSR builds with external CJS dependencies. Since Vite 5, the problem happens in development as well. You don't get any indication that it won't work in production. TypeScript doesn't complain either.

Solution

This plugin will automatically unwrap the default export from CJS dependencies that you specify during SSR builds. In other words, the following code:

import foo, { named, named2 as renamed } from "foo";

will be transformed into:

const {
  default: foo = __cjsInterop1__,
  named,
  named2: renamed,
} = __cjsInterop1__?.default?.default?.__esModule
  ? __cjsInterop1__.default.default
  : __cjsInterop1__?.default?.__esModule
    ? __cjsInterop1__.default
    : __cjsInterop1__;
import * as __cjsInterop1__ from "foo";

which takes care of unwrapping the default export and creating a synthetic default export if necessary.

The change for dynamic imports is more complicated, but allows the import() function to resolve to an object that not only resembles the standard ES6 namespace as expected, but also a CommonJS export:

const foo = await import("foo");

// ES6 namespace, with default export
foo.default.bar(); // Works

// CommonJS Module (some libraries expect this to work because webpack allows it)
foo.bar(); // Also works

Installation

npm install -D vite-plugin-cjs-interop

Usage

// vite.config.js
import { cjsInterop } from "vite-plugin-cjs-interop";

export default {
  plugins: [
    cjsInterop({
      // List of CJS dependencies that require interop
      dependencies: [
        "some-package",
        // Deep imports should be specified separately
        "some-package/deep/import",
        // But globs are supported
        "some-package/foo/*",
        // Even deep globs for scoped packages
        "@some-scope/**",
        // If you want to skip a specific package, you can use negative globs
        "!@donottransformme/**",
      ],
    }),
  ],
};

The matcher uses minimatch underneath, for more details on supported syntax.

Compatibility

We currently test the plugin end-to-end (both SSR and client, in both vite build and vite dev modes) against the latest patch of:

• Vite 5, 6, 7, and 8 — specifically the most recent release in the ~5, ~6.4, ~7.3, and 8 ranges.
• Node 22, 24, 25, and 26 on Linux; Node 24 on macOS and Windows.

Support policy

• For Vite, we try to follow Vite's own support window: the latest major plus the latest minor of each of the two preceding majors.
• For Node, we try to follow Node's own support window: latest patches of "LTS" and "current" releases.

Note that we still test against Vite 5 but it's not an officially supported version. We'll try to keep testing against it as long as it doesn't require any special handling.

License

MIT