CommonJS

If we're running in a CommonJS environment, the package cannot be required:

$ node -e 'require( "@wordpress/dataviews" );'
node:internal/modules/cjs/loader:647
      throw e;
      ^

Error [ERR_PACKAGE_PATH_NOT_EXPORTED]: No "exports" main defined in /tmp/test/node_modules/@wordpress/dataviews/package.json

This is particularly problematic when trying to test with jest, e.g.

const x = require( '@wordpress/dataviews' );

it( 'passes', () => {
    expect( true ).toBe( true );
} );

This fails with the following error:

    Cannot find module '@wordpress/dataviews' from 'foo.test.js'

    > 1 | const x = require( '@wordpress/dataviews' );
        |                                            ^
      2 |
      3 | it( 'passes', () => {
      4 |     expect( true ).toBe( true );

      at Resolver._throwModNotFoundError (node_modules/jest-resolve/build/resolver.js:427:11)
      at Object.<anonymous> (foo.test.js:1:44)

All this is because there is no commonjs export anymore after #66825, only types and import.

Adding a "require": "./build/index.js" or "default": "./build/index.js" at the end of the object makes it work.

ESM

Let's look at Jest first, running the following test with --experimental-vm-modules as documented at https://jestjs.io/docs/ecmascript-modules.

import * as x from '@wordpress/dataviews';

it( 'passes', () => {
    expect( true ).toBe( true );
} );

This fails with the following error: (with some irrelevant text snipped)

  ● Test suite failed to run

    Jest encountered an unexpected token

    Jest failed to parse a file. This happens e.g. when your code or its dependencies use non-standard JavaScript syntax, or when Jest is not configured to support such syntax.

    [...]

    Details:

    /tmp/test/node_modules/@wordpress/dataviews/build-module/index.js:1
    ({"Object.<anonymous>":function(module,exports,require,__dirname,__filename,jest){export { default as DataViews } from './components/dataviews';
                                                                                      ^^^^^^

    SyntaxError: Unexpected token 'export'

      at Runtime.createScriptFromCode (node_modules/jest-runtime/build/index.js:1505:14)

This is because the file at node_modules/@wordpress/dataviews/build-module/index.js is supposedly in CommonJS format, not ESM, but actually contains ESM code. There are two different ways you might fix this:

• Rename all the files under build-module/ to .mjs so they're parsed as ESM.
  • Also build-wp/index.js, since that contains ESM code too.
• Add "type": "module" to the package.json so all .js files default to being interpreted as ESM.
  • And then rename all the files under build/ to .cjs so they're parsed as CommonJS.

Trying to import it with node --input-type=module -e 'import * as dataviews from "@wordpress/dataviews";' has additional problems due to the stricter ECMAScript loader:

• It does not support folders as modules, directory indexes (e.g. './startup/index.js') must be fully specified.
• It does no extension searching. A file extension must be provided when the specifier is a relative or absolute file URL.

so even after applying the fixes above we still get failures like

Error [ERR_UNSUPPORTED_DIR_IMPORT]: Directory import '/tmp/test/node_modules/@wordpress/dataviews/build-module/components/dataviews' is not supported resolving ES modules imported from /tmp/test/node_modules/@wordpress/dataviews/build-module/index.mjs

But since this package is probably not intended to be used that way (and it works with webpack and jest), it's probably safe to ignore that.