// ==UserScript==
// @name         9gag - Scroll down to current position
// @namespace    https://github.com/Procyon-b
// @version      0.2
// @description  Scroll down back where the focus was when you clicked the arrow-up icon or scrolled up
// @author       Achernar
// @match        https://9gag.com/*
// @grant        none
// @downloadURL none
// ==/UserScript==

(function() {
"use strict";

var pos=[0,0], btt=document.querySelector('.back-to-top')

if (!btt) return;

window.addEventListener('scroll', savePos);

function savePos(r=0) {
  var d=window.scrollY - pos[1];
  if (d < 0) showHide(true);
  if (d >= 0) {
    pos=[window.scrollX, window.scrollY];
    showHide();
    }
  }

var disp=false;
function showHide(show=false) {
  if (show == disp) return;
  back.style.display= show?'':'none';
  disp=!disp;
  }

var back=document.createElement('a');

document.querySelector('header#top-nav').appendChild(back);

back.href='javascript:;';
back.classList='back-to-top';
back.style='transform: rotate(180deg); top: 5em; display: none;';
back.title='Scroll back to position';

back.addEventListener('click', function(e){
  if (pos) window.scrollTo.apply(null, pos);
  showHide();
  });

})();