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https://github.com/cmdcolin/using_esm_with_jest
https://github.com/cmdcolin/using_esm_with_jest
Last synced: 4 days ago
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- Host: GitHub
- URL: https://github.com/cmdcolin/using_esm_with_jest
- Owner: cmdcolin
- Created: 2024-03-16T15:31:11.000Z (8 months ago)
- Default Branch: master
- Last Pushed: 2024-03-16T15:44:13.000Z (8 months ago)
- Last Synced: 2024-04-15T02:14:37.773Z (7 months ago)
- Language: JavaScript
- Size: 39.1 KB
- Stars: 0
- Watchers: 2
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
Awesome Lists containing this project
README
# jest with esm
Test using a pure-ESM module dependency (`quick-lru`) in jest
We are using `"type":"module"` in this module's package.json, which marks this
module as pure-ESM, and then allows us to consume other pure-ESM modules. This
is the most canonical setup
## The command line flag that makes it work
```bash
$ NODE_OPTIONS="$NODE_OPTIONS --experimental-vm-modules" yarn test
yarn run v1.22.22
warning package.json: No license field
$ jest
(node:409041) ExperimentalWarning: VM Modules is an experimental feature and might change at any time
(Use `node --trace-warnings ...` to show where the warning was created)
PASS src/lru.test.js
✓ testing (1 ms)
Test Suites: 1 passed, 1 total
Tests: 1 passed, 1 total
Snapshots: 0 total
Time: 0.136 s
Ran all test suites.
Done in 0.50s.
```
## Fails without that command line flag
```bash
yarn test
yarn run v1.22.22
warning package.json: No license field
$ jest
FAIL src/lru.test.js
● 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.
Out of the box Jest supports Babel, which will be used to transform your files into valid JS based on your Babel configuration.
By default "node_modules" folder is ignored by transformers.
Here's what you can do:
• If you are trying to use ECMAScript Modules, see https://jestjs.io/docs/ecmascript-modules for how to enable it.
• If you are trying to use TypeScript, see https://jestjs.io/docs/getting-started#using-typescript
• To have some of your "node_modules" files transformed, you can specify a custom "transformIgnorePatterns" in your config.
• If you need a custom transformation specify a "transform" option in your config.
• If you simply want to mock your non-JS modules (e.g. binary assets) you can stub them out with the "moduleNameMapper" config option.
You'll find more details and examples of these config options in the docs:
https://jestjs.io/docs/configuration
For information about custom transformations, see:
https://jestjs.io/docs/code-transformation
Details:
/home/cdiesh/t1/src/lru.test.js:1
({"Object.":function(module,exports,require,__dirname,__filename,jest){import makeLRU from "./lru";
^^^^^^
SyntaxError: Cannot use import statement outside a module
at Runtime.createScriptFromCode (node_modules/jest-runtime/build/index.js:1505:14)
Test Suites: 1 failed, 1 total
Tests: 0 total
Snapshots: 0 total
Time: 0.139 s, estimated 1 s
Ran all test suites.
error Command failed with exit code 1.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.
```
## Reference
https://jestjs.io/docs/ecmascript-modules