Synchronous scrolling

script.js

let isSyncingLeftScroll = false;
let isSyncingRightScroll = false;

document.getElementById('input_table').addEventListener('scroll', e => {
  if (!isSyncingLeftScroll) {
    isSyncingRightScroll = true;
    document.getElementById('output_table').scrollTop = e.target.scrollTop;
  }
  isSyncingLeftScroll = false;
}, false);
document.getElementById('output_table').addEventListener('scroll', e => {
  if (!isSyncingRightScroll) {
    isSyncingLeftScroll = true;
    document.getElementById('input_table').scrollTop = e.target.scrollTop;
  }
  isSyncingRightScroll = false;
}, false);