How I fixed the unexpected token error in Jest

Question

With the help of a code example, can you tell me how I fixed the unexpected token error in Jest?

Answer 1

To resolve this issue , you need to ensure that the testing framework is correctly set up to handle the specific syntax or modules in your project. Let's see the steps:

Check Your jest.config.js:

If you’re using TypeScript or JSX, ensure the transform property is set up to use ts-jest or babel-jest. Example configuration:

module.exports = {

  transform: {

    "^.+\\.(ts|tsx|js|jsx)$": "babel-jest",

  },

  transformIgnorePatterns: ["node_modules/(?!(module-to-transform)/)"],

};

This helps Jest transpile files before running tests​

Update Babel Configuration:

Include the required presets in your babel.config.js for React and TypeScript:

presets: [

  "@babel/preset-env",

  "@babel/preset-react",

  "@babel/preset-typescript",

];

This ensures compatibility with JSX and modern JavaScript syntax​

Adjust transformIgnorePatterns:

Add a transformIgnorePatterns field to transpile necessary modules from node_modules. This is useful for libraries that distribute untranspiled code​

Check TypeScript Configuration:

Ensure your tsconfig.json has the correct jsx property set, e.g., "jsx": "react-jsx" or "jsx": "preserve" if using TypeScript​

Clear Jest Cache and Debug:

Run the following commands to clear the Jest cache and identify any further issues:

npx jest --clearCache

npx jest –verbose