I'm currently working on writing Jest tests for my TypeScript code. To ensure compatibility with older browsers, I have included some polyfills and other necessary imports for side effects.
Here is a snippet of my code (variables changed for anonymity):
src/my_code.ts
import i18next from "i18next";
import Backend from 'i18next-http-backend';
import "promise-polyfill/src/polyfill";
var someVar = 12;
export function someFunc() {
return someVar + 1;
}
Below is a glimpse of my test script:
test/my_code.test.ts
import { someFunc } from '../src/my_code';
describe('some test case', function () {
console.log(someFunc());
});
Although I believe my package.json and jest.config.js settings are correct, when I run the test, I encounter the following error:
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.
• 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:
my_code/node_modules/promise-polyfill/src/polyfill.js:1
({"Object.<anonymous>":function(module,exports,require,__dirname,__filename,jest){import Promise from './index';
^^^^^^
SyntaxError: Cannot use import statement outside a module
1 | import i18next from "i18next";
2 | import Backend from 'i18next-http-backend';
> 3 | import "promise-polyfill/src/polyfill";
| ^
at Runtime.createScriptFromCode (node_modules/jest-runtime/build/index.js:1479:14)
at Object.<anonymous> (src/my_code.ts:3:1)
Test Suites: 1 failed, 1 total
Tests: 0 total
Snapshots: 0 total
Time: 1.701 s
Ran all test suites.
npm ERR! Test failed. See above for more details.
While other imported modules in my code are functioning properly, the ones causing issues are utilizing import x from "y"; syntax for side effects rather than import "z";.
Any suggestions on possible solutions to this problem?
EDIT: Here is my jest.config.js:
module.exports = {
transform: { '^.+\\.ts?$': 'ts-jest' },
testEnvironment: 'node',
testRegex: '/test/.*\\.(test|spec)?\\.(ts|tsx)$',
moduleFileExtensions: ['ts', 'tsx', 'js', 'jsx', 'json', 'node']
};