CODEWITHSUNDEEP
javascriptnode.jstypescriptjestjses6-modules
Gabriel Braga Estefanski
Gabriel Braga Estefanski

Reputation: 9

Jest Crashes When Importing JSON File with assert { type: 'json' }

This is my Jest configurations:

import type { Config } from 'jest'

const config: Config = {
  testEnvironment: 'node',
  transform: {
    '^.+\\.ts$': 'ts-jest',
    '^.+\\.js$': 'babel-jest',
  },
  moduleFileExtensions: ['ts', 'js'],
  transformIgnorePatterns: ['/node_modules/'],
  extensionsToTreatAsEsm: ['.ts'],
}

export default config

And this is my typescript configuration in the tsconfig.ts:

{
  "compilerOptions": {
    "target": "es2021",
    "module": "ESNext",
    "rootDir": "./src",
    "moduleResolution": "Node10",
    "baseUrl": "./src",
    "paths": {
      "*": ["*", "src/*"]
    },
    "resolveJsonModule": true,
    "outDir": "./dist",
    "esModuleInterop": true,
    "forceConsistentCasingInFileNames": true,
    "strict": true,
    "noImplicitAny": true,
    "strictNullChecks": true,
    "strictFunctionTypes": true,
    "strictBindCallApply": true,
    "strictPropertyInitialization": true,
    "noImplicitThis": true,
    "useUnknownInCatchVariables": true,
    "alwaysStrict": true,
    "noUnusedLocals": true,
    "exactOptionalPropertyTypes": true,
    "noImplicitReturns": false,
    "noFallthroughCasesInSwitch": true,
    "noUncheckedIndexedAccess": true,
    "noImplicitOverride": true,
    "skipLibCheck": true
  },
  "include": ["src/**/*.ts", "src/utils/excelGenerator.ts", "src/__tests__/app.test.ts"],
  "files": ["src/types.d.ts"]
}

Log when I try to execute npm run test:

src/app.ts:6:50 - error TS2821: Import assertions are only supported when the '--module' option is set to 'esnext', 'nodenext', or 'preserve'.

6 import swaggerFile from '../swagger-output.json' assert { type: 'json' }; ~~~~~~~~~~~~~~~~~~~~~~~

Test Suites: 2 failed, 2 total Tests: 0 total Snapshots: 0 total Time: 3.366 s Ran all test suites.

Upvotes: 0

Views: 123

Answers (1)

Estus Flask
Estus Flask

Reputation: 223259

The error describes the problem, TypeScript supports assert only for native ESM with specific target.

For Jest with native ESM, both extensionsToTreatAsEsm Jest option and --experimental-vm-modules Node option have to be used, which is presumably done here. A certain TS config needs to be provided in Jest:

  '^.+\\.ts$': [
    'ts-jest',
    {
      tsconfig: {
        module: 'NodeNext',
        moduleResolution: 'Node16',
      },
    },
  ],

For Jest with CJS, which is more commonly occurring setup, this may require to add Babel to transforms to process compiled native ESMs further, no extensionsToTreatAsEsm option should be used. This requires jest-chain-transform, @babel/preset-env and @babel/plugin-syntax-import-attributes to be installed, with multiple Jest transforms being chained:

'^.+\\.ts$': [
  'jest-chain-transform', {
    transformers: [
      [
        'ts-jest',
        {
          tsconfig: {
            module: 'NodeNext',
            moduleResolution: 'Node16',
          },
        },
      ],

      ['babel-jest', {
        presets: [
          [
            '@babel/preset-env',
            {
              targets: { node: 'current' }
            }
          ]
        ],
        plugins: [
          [
            '@babel/plugin-syntax-import-attributes',
            { deprecatedAssertSyntax: true }
          ]
        ]
      }]
    ]
  }
],

Notice that assert has been deprecated in favour of with.

Upvotes: 0

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