Jest fails with “Unexpected token *” on import statement

Question

Why does Jest fail with \"Unexpected token *\" on a simple import statement...

Error log:

Admin@Admin-PC MINGW32 /d/project (master)
$ npm         


        

Answer 1

I am using react-native-web and the fix for my issue was to add the react-native-web preset to my jest.config.js:

module.exports = {
transform: {
  '^.+\\.tsx?$': 'ts-jest',
},
timers: 'fake',
testPathIgnorePatterns: [
  '<rootDir>/build/',
  '<rootDir>/node_modules/',
  '<rootDir>/rndemo/build/',
],
globals: {
  'ts-jest': {
    diagnostics: {
      warnOnly: true,
    },
  },
},
preset: 'react-native-web',
}

Answer 2

I had a similar issue on a React + Typescript app.

The first mistake I made was to define the jest.config.js as jest.config.ts

Running on Node v12.latest

Then the configuration that worked for me were the following:

// jest.config.js

module.exports = {
  preset: "ts-jest",
  testEnvironment: "node",
  roots: ["./src"],
  transform: { "\\.ts$": ["ts-jest"] },
  testRegex: "(/__tests__/.*|(\\.|/)(test|spec))\\.tsx?$",
  moduleFileExtensions: ["ts", "tsx", "js", "jsx", "json", "node"],
  globals: {
    "ts-jest": {
      tsConfig: {
        // allow js in typescript
        allowJs: true,
      },
    },
  },
};

// tsconfig.json
{
  "compilerOptions": {
    "target": "es5",
    "lib": ["dom", "dom.iterable", "esnext"],
    "allowJs": true,
    "skipLibCheck": true,
    "esModuleInterop": true,
    "allowSyntheticDefaultImports": true,
    "strict": true,
    "forceConsistentCasingInFileNames": true,
    "module": "esnext",
    "moduleResolution": "node",
    "resolveJsonModule": true,
    "isolatedModules": true,
    "noEmit": true,
    "jsx": "react",
    "baseUrl": "."
  },
  "include": ["src"],
  "exclude": ["node_modules", "**/*.spec.ts"]
}

// package.json
"devDependencies": {
    "@types/jest": "^26.0.5",
    "jest": "^26.1.0",
    "ts-jest": "^26.1.3"
}

Answer 3

As it has been said, some modules needs to be transpiled, & some don't. Here is a regex I use that work in a lot of projects

  "jest": {
    "preset": "react-native",
    "transformIgnorePatterns": [
      "node_modules/(?!(jest-)?react-native|react-(native|universal|navigation)-(.*)|@react-native-community/(.*)|@react-navigation/(.*)|bs-platform|(@[a-zA-Z]+/)?(bs|reason|rescript)-(.*)+)"
    ]
  }

It's working for most common react native thing, & include also a specific package (here bs-platform) as an example, when isn't captured by previous patterns.

Answer 4

Some react-native libraries ship uncompiled ES6 code.

ES6 code needs to be compiled before it can be run by Jest.

The Jest doc about Testing React Native Apps includes a section about compiling dependencies that don't ship pre-compiled code.

You will need to tell Jest to compile react-navigation-tabs by whitelisting it in the transformIgnorePatterns option in your Jest config.

Example:

Changing the jest.config.js file into something like below, fixed the issue mentioned in OP.

But the "react-native-reanimated" module (which requires native integration, as described in another post) needs further work, and we should Mock modules with such native requirements...

module.exports = {
  preset: 'react-native',
  moduleFileExtensions: ['ts', 'tsx', 'js', 'jsx', 'json', 'node'],
  transformIgnorePatterns: [
    "node_modules/(?!(react-native"
      + "|react-navigation-tabs"
      + "|react-native-splash-screen"
      + "|react-native-screens"
      + "|react-native-reanimated"
    + ")/)",
  ],
}

Note: the transformIgnorePatterns option (which is an array of Regular-Expressions) is originally meant to exclude files from being compiled, but using (?!(some-dir-name|another-name)) pattern (the (?!...), negative look-ahead), we do tell Jest to exclude anything in node_modules directory, except the names that we did specify.

Answer 5

Somewhere in your config file (.babelrc.js or package.json) you have to have "modules" under "presets" set to one of the "amd" | "umd" | "systemjs" | "commonjs" | "cjs" | "auto" | false.

referer this fragment from the documentation

something like this:

    "presets": [
  [
    "@babel/preset-env", {
      "targets": process.env.BABEL_TARGET === 'node' ? {
        "node": 'current'
      } : {
        "browsers": [ "last 2 versions" ]
      },
      "loose": true,
      "modules": 'commonjs'
    }
  ]
]