background.js

const second = 1000;
const variate = second * 10;

function httpGetAsync(url, callback) {
  let xmlHttp = new XMLHttpRequest();
  xmlHttp.onreadystatechange = () => {
    if (xmlHttp.readyState == 4 && xmlHttp.status == 200)
      callback(xmlHttp.responseText);
  }
  xmlHttp.open('GET', url, true);
  xmlHttp.send(null);
}

function trySendRequestLoop() {
  let time = second * 50 + Math.floor(Math.random() * variate);
  chrome.tabs.query({
  }, (tabs) => {
    for (let tab of tabs) {
      let url = tab.url;
      if (url.includes('vaje.um.si') || url.includes('vaje.uni-mb.si')) {
        httpGetAsync('https://vaje.um.si/vaje/new/vaje.jsp', (data) => console.log('ping send!'));
        return;
      }
    }
    console.log('vaje uni not found in tabs!');
  });

  console.log(`resending in ${time / 1000} seconds!`);
  setTimeout(trySendRequestLoop, time);
}

trySendRequestLoop();