return {
    /* config options for all phases except development here */
  }
}The commented lines are the place where you can put the configs allowed by next.config.js, which are defined in this file.However, none of the configs are required, and it's not necessary to understand what each config does. Instead, search for the features you need to enable or modify in this section and they will show you what to do.
Avoid using new JavaScript features not available in your target Node.js version. next.config.js will not be parsed by Webpack, Babel or TypeScript.