When will this error occur? You may get this error while you're running unit tests in React (TypeScript) . Fix? - Run, > npm i webpack > npm i --save-dev @babel/preset-env @babel/preset-react @babel/preset-typescript @babel/plugin-proposal-class-properties - Create a .babelrc file in root folder (next to package.json ) - Update the .babelrc file as follows: { "presets": [ "@babel/preset-env", "@babel/preset-react", "@babel/preset-typescript" ], "plugins": [ "@babel/plugin-proposal-class-properties" ] } - Run, > jest The tests will run without errors Courtesy