FacebookInvitator.js

function check() {
  fb_checks = document.querySelectorAll('a[role="checkbox"]'); 
  
  for(i = 0; i < fb_checks.length; i++) {
    if(fb_checks[i].getAttribute('aria-checked') == 'false') {
      fb_checks[i].click();
    }
  }
}

var btn = document.createElement('button'); 	
btn.id = 'hack-btn';
btn.innerText='INVITE';
//CSS styles
btn.setAttribute("style", 
"position: fixed; top: 8px; left: 5px; z-index: 999; background-color: black; color: white; cursor: pointer");

document.body.appendChild(btn);

var button = document.querySelector('#hack-btn');
button.addEventListener('click', function() {check()}, false);