Construir librerías

Dejo el codigo utilizado durante la clase:

import { defineConfig, loadEnv } from 'vite'
import { resolve, dirname, format } from 'path'
import { fileURLToPath } from 'url'

const _dirname = typeof __dirname !== 'undefined'
  ? __dirname
  : dirname(fileURLToPath(import.meta.url))
/** @type {import('vite').UserConfig} */
export default defineConfig(({command, mode})=>{
    const env = loadEnv(mode, process.cwd());

    const port = env.VITE_PORT;

    console.log(command, mode)
  
    if (mode === "development") {
        console.log("modo desarrollo")
        return {
            server:{
                port
            }
        }
    } else {
        console.log("modo produccion")
        return {
            build:{
               lib: {
                entry: resolve(_dirname, 'lib', 'main.js'),
                name: 'demo',
                fileName: (format)=>`demo.${format}.js`
               }
            }
        }
    }
})