Nativefier/app/src/static/login/login.js

import electron from 'electron';
const {ipcRenderer} = electron;

const form = document.getElementById('login-form');

form.addEventListener('submit', event => {
    event.preventDefault();
    const username = document.getElementById('username-input').value;
    const password = document.getElementById('password-input').value;
    ipcRenderer.send('login-message', [username, password]);
});