I'm working the first time with the combination Svelte and Electron and got some trouble in understanding the following behavior about the preload.mjs and ES-Module/CommonJS.

My project is configured with "type"="module" in package.json - which means I have to use import-statements instead of require (as far as I understood).

So following preload.mjs did I build (and it worked without any errors in the DevTools until today):

import { contextBridge, ipcRenderer } from "electron";

contextBridge.exposeInMainWorld('electron', {
    prisma: {
        addRecord: async (data) => {
            return ipcRenderer.invoke('prisma:add-record', data); 
        },
        getAll: async () => {
            return ipcRenderer.invoke('prisma:get-all'); 
        },
    }
});

Now I tried to add a new function like that:

import { contextBridge, ipcRenderer } from "electron";
contextBridge.exposeInMainWorld('electron', {
    prisma: {
        addRecord: async (data) => {
            return ipcRenderer.invoke('prisma:add-record', data); 
        },
        getAll: async () => {
            return ipcRenderer.invoke('prisma:get-all'); 
        },
    },
    export: {
        export_csv: async(file_name, content) => {
            return ipcRenderer.invoke('export:save-csv', {file_name, content});
        },
    },
});

But now nothing works anymore... I just get error messages like:

Unable to load preload script: /home/.../frontend/electron/preload.mjs
SyntaxError: Cannot use import statement outside a module
    at runPreloadScript (VM214 sandbox_bundle:2:151981)
    at VM214 sandbox_bundle:2:152300
    at VM214 sandbox_bundle:2:152455
    at ___electron_webpack_init__ (VM214 sandbox_bundle:2:152459)
    at VM214 sandbox_bundle:2:152582

After searching a lot in my code and google I just tried to change the import to

const {ipcRenderer} = require('electron/renderer')
const {contextBridge} = require('electron')

And now: all errors are gone away and the app just worked as before. I do not really understand what happens here and why.

Anyone here who can explain this to me? I really want to now what happened and what I did wrong.