.flat is not a function only with jest

Question

When running my tests with jest, I had the above error;

Error: Uncaught [TypeError: array.map(...).flat is not a function]

Following the solution from that issue, https://github.com/kulshekhar/ts-jest/issues/828

I've installed core-js on dependencies and putting this in jest.config.js

setupFiles: ['core-js'],

I'd receive that another error;

Error: Uncaught [Error: Not supported]

And this is occurring only with jest, I'm using babel and webpack on my application and storybook without errors on flat.

My jest.config.js

const PATH = require('./path')

module.exports = {
  setupFilesAfterEnv: ['./rtl.setup.js'],
  moduleFileExtensions: ['js'],
  verbose: true,
  moduleNameMapper: {
    '@components(.*)$': `${PATH.source}/components/$1`
  },
  transform: {
    '^.+\\.js$': 'babel-jest'
  }
}

Answer 1

This error happens if your node version is old. Try to update it to the latest version.

Answer 2

per https://github.com/kulshekhar/ts-jest/issues/828#issuecomment-433976880

this problem can be solved by running

npm install --save-dev core-js

and adding core-js to your jest config's setupFiles

"setupFiles": ["core-js"]