jest fails to import the import of my import which is causing npm run test command to fail with SyntaxError: Unexpected token 'export' at first line of my bar.ts file. For this example foo.js is a local file, not a node module. I can change foo.js to foo.ts and change the import in bar.ts but that is not the solution.
Files in my src folder:
foo.js:export const magicNumber = 42;
bar.ts:import { magicNumber } from './foo.js';
export const secondMagicNumber = magicNumber / 2;
bar.test.ts:import { secondMagicNumber } from './bar';
import assert from 'assert';
it('should work', function() {
assert.strictEqual(secondMagicNumber, 21);
});
Files in the root folder:
jest.config.js:export default {
preset: 'ts-jest',
testEnvironment: 'node',
};
package.json:{
"name": "testing-with-jest",
"version": "1.0.0",
"description": "",
"scripts": {
"test": "jest"
},
"author": "",
"license": "ISC",
"devDependencies": {
"@types/jest": "^26.0.20",
"jest": "^26.6.3",
"ts-jest": "^26.5.2",
"typescript": "^4.2.2"
},
"type": "module"
}
tsconfig.json:{
"compilerOptions": {
"target": "ESNext",
"module": "ESNext",
"outDir": "./dist",
"strict": true,
"esModuleInterop": true,
"skipLibCheck": true,
"forceConsistentCasingInFileNames": true,
"declaration": true,
"moduleResolution": "node"
},
"include": ["./src/**/*.ts"]
}
So the problem is that both ts-jest and jest are tricky to set up for the ES6 import/export syntax. I did exactly that by:
jest and ts-jest >= 27.0.0 versions.tsconfig.json:
{
"compilerOptions": {
"esModuleInterop": true,
"allowJs": true
}
}
jest.config.ts:
export default {
globals: {
extensionsToTreatAsEsm: ['.ts', '.js'],
'ts-jest': {
useESM: true
}
},
preset: 'ts-jest/presets/js-with-ts-esm',
// from https://stackoverflow.com/a/57916712/15076557
transformIgnorePatterns: [
'node_modules/(?!(module-that-needs-to-be-transformed)/)'
]
}