"SyntaxError: Cannot use import statement outside a module" when importing a module which imports a module for side effects in Jest

Question

I'm trying to use Jest to test some TS code I've written. I need this code to work on older browsers so am importing some polyfills and such for side effects.

My code looks something like this (variables changed to be more generic):

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;
}

And my test looks something like this:

test/my_code.test.ts

import { someFunc } from '../src/my_code';

describe('some test case', function () {
    console.log(someFunc());
});

I think my package.json and jest.config.js are okay, but running the test gives:

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.

The other modules I've imported in my source work, but these are using the import x from "y"; syntax rather than import "z"; for side effects. Anything here I could try?

EDIT: Added jest.config.js below:

module.exports = {
    transform: { '^.+\\.ts?$': 'ts-jest' },
    testEnvironment: 'node',
    testRegex: '/test/.*\\.(test|spec)?\\.(ts|tsx)$',
    moduleFileExtensions: ['ts', 'tsx', 'js', 'jsx', 'json', 'node']
};

user16730065 · Accepted Answer · 2021-08-24 20:47:02Z

1

Come on brotha, please show me yow jest.config file also yow app works with them import statements, bcuz there might be something bundling yow code up to a point it is understandable to the environment it runs, but on the other head you is running them tests files with nodejs and as you already see, node doesn’t understand that, plus adding the fact that them test cases are written in ts instead of js, try this first, if it doesn’t work I’ll need yow jest config.

Install ts-node.

If you want to execute some ts code ether you need yo compile them files first or you can install ts-node

npm i -D ts-node.

To run them tests you need ts-node ./path-to-yow-file.

I think there is already a package call ts-jest

answered Aug 24, 2021 at 20:47

user16730065

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1 Comment

user2078994 Over a year ago

Thanks, I've just added the Jest config to the original question

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"SyntaxError: Cannot use import statement outside a module" when importing a module which imports a module for side effects in Jest

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Install ts-node.

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Install ts-node.

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