One solution: add to the top of your main JavaScript file: import 'regenerator-runtime/runtime' Parcel will include this package by default, increasing the size of is not defined ReferenceError: regeneratorRuntime is not defined This is where the regenerator-runtime library comes in. Have a question about this project? Why Does the ReferenceError: RegeneratorRuntime is Not Defined Error Occur? The point of packages such as create-react-app is to save a tremendous amount of hassle setting up a working Webpack configuration yourself. to your account. One of the most popular features of JavaScript is the ability to write asynchronous code using async/await functions. Secure your code as it's written. Just add: