Dealing with ES Modules "Cannot create property 'prependPath' on boolean 'true'"

[AStoker]

Originally opened/closed here (without resolution) #9266

This is more of a PSA/help for any poor soul in the future who runs into this.

I had upgrade my node server to the LTS (22.13.0) when I noticed this bug happening. I'm using Angular 19 with a proxy config file that had previously worked with Node 20.
Upon inspection, I had specifically been using an ES module format (export default {...}) with my file proxy.config.js which was passed along to Vite. However, somewhere in the process, because this was being treated as a module, the "object" that was returned/passed to Vite was like this

{
   __esModule: true,
   default: {
      ... // options
   }
}

The options that should have been passed to vite were inside the default property, but when vite started parsing the module as a whole, it got held up at the __esModule boolean, which ultimately caused the problem.

The resolution for me was to rename the config file to use the .mjs extension. Alternatively I could have used the .json extension, but because I needed function definitions, I required .mjs.