How to fix Jest ‘encountered an unexpected token import’ error with JavaScript?

To fix Jest ‘encountered an unexpected token import’ error with JavaScript, we set the Jest config to allow modules.

For instance, in jest.config.js, we write

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: {
        allowJs: true,
      },
    },
  },
};

to allow extensions for modules by setting moduleFileExtensions to ["ts", "tsx", "js", "jsx", "json", "node"].

We set allowJs to true to allow JavaScript code to run including modules.

And we set transform to { "\\.ts$": ["ts-jest"] } to transform them with ts-jest so they can be run with Jest.