NodeJS Ajax requests working exactly seven times

I'm currently learning JavaScript / NodeJS / electron, and I want to build a small presenter-app to remotely control powerpoint-presentations.

I've setup a server using electron like this:

const electron = require('electron');
const robot = require("robotjs");
const fs = require('fs');
const express = require('express');
const cors = require('cors');

const {
  app,
  BrowserWindow
} = electron;

var mainWin = null;
var contentString;

app.on('ready', function() {
  mainWin = new BrowserWindow({
    width: 800,
    height: 600
  });

  contentString = "";

  // Remove Menu-Bar
  mainWin.setMenu(null);

  const port = 3000;

  var app = express();
  app.use(cors());

  app.post('/remote/forward', function(request, response, next) {
    var ip = getRemoteIP(request);
    log(mainWin, "presenter - forward");
    robot.keyTap("right");
  });

  app.post('/remote/backward', function(request, response, next) {
    var ip = getRemoteIP(request);
    log(mainWin, "presenter - backward");
    robot.keyTap("left");
  });


  app.listen(port, function() {
    log(mainWin, 'server listening on port ' + port);
  });
});


function log(mainWin, text) {
  contentString += getFormattedDate() + " " + text;
  contentString += "<br />";
  mainWin.loadURL("data:text/html;charset=utf-8," + encodeURI(contentString));
}

I call these with two js-functions:

function sendForwardRequest() {
  $.ajax({
    type: 'POST',
    data: {
         blob: {action:"forward"}
     },
    contentType: "application/json",
    dataType: 'json',
    url: 'http://192.168.2.110:3000/remote/forward',
    success: function(data) {
      console.log('success');
    },
    error: function(error) {
      console.log("some error in fetching the notifications");
    }
  });
}

function sendBackwardRequest() {
  $.ajax({
    type: 'POST',
    data: {
         blob: {action:"backward"}
     },
    contentType: "application/json",
    dataType: 'json',
    url: 'http://192.168.2.110:3000/remote/backward',
    success: function(data) {
      console.log('success');
    },
    error: function(error) {
      console.log("some error in fetching the notifications");
    }
  });
}

I'm sure that this solution is quite miserble, as I said, I'm currently learning this. My question now is: This works for exactly seven times. After that, I have to reload my clients browser. How can I fix this? Also, what would be a better solution for the requests? I'd like to have only one app.post()-method and use the given post-parameters instead. Last question: What could be a nicer method for the logging? I'd like to append content to my window instead of having to reload the whole string each time.

Thank you very much!

via Marcel