Support named exports

When using CSS modules with named exports (e.g. you’re using Typescript and typings-for-css-modules-loader), they look like:

export const foo = 'foo';
export const barBaz = 'barBaz';

And the consumer uses as:

import * as styles from './styles.css';

...
<div className={styles.barBaz} />

This mock does not play nice. I’ve found that returning true for the __esModule check here does work - essentially saying that our mocked module is an ES module and the keys are the named exports.

Any ideas if and how this project could accommodate that? E.g. using identity-obj-proxy/esm?

[joaovieira]

@gabsprates @john-d-pelingo sorry for not answering here, what I did was to define my own css mock with the modified identity-obj-proxy as mentioned above:

// .jest/identity-obj-proxy-esm.js

// Modified identity-obj-proxy.

// This works around the fact we use ES named exports for styles, e.g.:
// import * as styles from './styles.scss'.
// https://github.com/keyanzhang/identity-obj-proxy/issues/8
module.exports = new Proxy(
  {},
  {
    get: function getter(target, key) {
      if (key === '__esModule') {
        // True instead of false to pretend we're an ES module.
        return true;
      }
      return key;
    },
  },
);

// jest.config.js

module.exports = {
  ...
  moduleNameMApper: {
    '\\.(jpg|jpeg|png|gif|webp|svg)$': 'identity-obj-proxy',
    '\\.(css|scss)$': '<rootDir>/.jest/identity-obj-proxy-esm.js',
  }
};

[nicolashemonic]

Hello guys,

Thank you all to share your solution.

There is a very more simple solution to make work Jest + Typescript + Css Module in 2020.

Typescript compilation typings-for-css-modules-loader is a deprecated tool that can be replaced by the Typescript plugin typescript-plugin-css-modules. The main advantage is that this plugin generate “hidden” definition file on the fly for each css module. All the stuff is totally managed by the compiler itself (not Webpack).

Test snapshot Along these versions: jest 25.5 ts-Jest 25.5 identity-obj-proxy 3.0

You don’t need to modify identity-obj-proxy. The problem you know is that Typescript not generate a default export for all class names. To fix that you just need two things:

1/ Set the esModuleInterop option of Typescript to true (you can remove allowSyntheticDefaultImports that will be enabled). And replace all of your import * as style from "./component.module.css" with import style from "./component.module.css". The compiler will generate for the compilation a helper that allow to retrieve all named export in a default one.

2/ Add the definition file created for typescript-for-css-modules here into the files property of the tsconfig.json. For example a dedicated tsconfig.json for ts-jest that extends the app one:

{
    "extends": "../tsconfig",
    "files": [
        "../app/types/css-module.d.ts"
    ]
}

This file allow the Typescript compiler to understand the import of the Css file and proceed to the compilation before the test.

Test Result Finally the snapshot contains the class names:

// Jest Snapshot v1, https://goo.gl/fbAQLP

exports[`<PrettyGraph /> rendering should display current situation 1`] = `
<p
  className="hello-world"
>
  Hello World!
</p>
`;

I hope that help!