How do I convert web application into desktop executable?

Electron is the easiest way:

1. Install electron

2. Create and edit main.js:

const electron = require('electron');
const { app, BrowserWindow } = electron;

let mainWindow;

app.on('ready', () => {
    mainWindow = new BrowserWindow({
        width: 1000,
        height: 700
    });

    mainWindow.setTitle('title of the desktop app');
    mainWindow.loadURL('http://www.yourwebpage.com');

    mainWindow.on('closed', () => {
        mainWindow = null;
    });
});

3. Execute desktop app:

electron main.js

And to build the app, use a builder such as electron-builder.

Hope that helps you!