main.js

const { app, BrowserWindow, ipcMain } = require('electron');
//ipcMain.on will receive the “btnclick” info from renderprocess 
ipcMain.on("btnclick", function(event, arg) {
   var url = "https://www.google.com"; 
    // inform the render process that the assigned task finished. 
    // event.sender.send in ipcMain will return the reply to renderprocess
    event.sender.send("btnclick-task-finished", url);
});