Separation of concerns will be your number one priority here. To achieve this, you can use setters and getters.

Remember, when Node first require's a module, it is also cached. Let's use this advantage as a form of state management.

Prior to separating / refactoring your code, you will find that your main.js file can grow to an enormous size. Using techniques such as this will allow you to split up your code into easily manageable, readable, single responsibility segments of code.

If you haven’t done so already, let's move construction of your mainWindow out of the main.js file and into its own file.

main.js (main thread)

// Import the necessary Electron modules.
const electronApp = require('electron').app;
const electronBrowserWindow = require('electron').BrowserWindow;

// Import the necessary Node modules.
const nodePath = require('path');

// Import the necessary Application modules.
const appMainWindow = require(nodePath.join(__dirname, 'main-window'));

// Prevent garbage collection.
let mainWindow = null;

// Application is now ready to start.
electronApp.on('ready', () => {
    mainWindow = appMainWindow.create();
});

// Re-activate Application when in macOS dock.
electronApp.on('activate', () => {
    if (electronBrowserWindow.getAllWindows().length === 0) {
        appMainWindow.create(mainWindow);
    }
});

// Close Application completely if not on macOS.
electronApp.on('window-all-closed', () => {
    if (process.platform !== 'darwin') {
        electronApp.quit();
    }
});

Having management of the mainWindow object in its own file separates our code into more readable and manageable chunks.

main-window.js (main thread)

// Import the necessary Electron modules.
const electronBrowserWindow = require('electron').BrowserWindow;

// Define the main window.
let mainWindow;

// Create the main window.
function create() {
    mainWindow = new electronBrowserWindow({
        x: 0,
        y: 0,
        width: 800,
        height: 600,
        show: false,
        webPreferences: {
            nodeIntegration: false,
            contextIsolation: true,
            preload: nodePath.join(__dirname, 'preload.js')
        }
    });

    // Load the main window.
    mainWindow.loadFile(nodePath.join(__dirname, 'main-window.html'))
        .then(() => { mainWindow.show(); })
        
    return mainWindow;
}

// Get the main window object.
function get() {
    return mainWindow;
}

// Export the publicly available functions.
module.exports = {create, get};

Finally, in your file (or any other file) that requires reference to your mainWindow object, just require your main-window.js file and call the get() function.

any-file (main thread)

// Import the necessary Node modules.
const nodePath = require('path');

// Import the necessary Application modules.
const appMainWindow = require(nodePath.join(__dirname, 'main-window'));

// Lets use it.
appMainWindow.get().webContents.send("search", recordset.recordset);