<div contenteditable>012345<br><br><br>9012345</div>

function getCaret(el) {
  let start, end;
  const range = document.getSelection().getRangeAt(0),
    preSelectionRange = range.cloneRange(),
    postSelectionRange = range.cloneRange();
  preSelectionRange.selectNodeContents(el);
  preSelectionRange.setEnd(range.startContainer, range.startOffset);
  postSelectionRange.selectNodeContents(el);
  postSelectionRange.setEnd(range.endContainer, range.endOffset);
  start = preSelectionRange.toString().length;
  end = start + range.toString().length;
  // count <br>'s and adjust start & end
  if (start > 0) {
    var node,
      i = el.children.length;
    while (i--) {
      node = el.children[i];
      if (node.nodeType === 1 && node.nodeName === 'BR') {
        start += preSelectionRange.intersectsNode(el.children[i]) ? 1 : 0;
        end += postSelectionRange.intersectsNode(el.children[i]) ? 1 : 0;
      }
    }
  }
  return {start, end};
}

function setCaret(el, start, end) {
  var node, i, nextCharIndex, sel,
    charIndex = 0,
    nodeStack = [el],
    foundStart = false,
    stop = false,
    range = document.createRange();
  range.setStart(el, 0);
  range.collapse(true);
  while (!stop && (node = nodeStack.pop())) {
    // BR's aren't counted, so we need to increase the index when one
    // is encountered
    if (node.nodeType === 1 && node.nodeName === 'BR') {
      charIndex++;
    } else if (node.nodeType === 3) {
      nextCharIndex = charIndex + node.length;
      if (!foundStart && start >= charIndex && start <= nextCharIndex) {
        range.setStart(node, start - charIndex);
        foundStart = true;
      }
      if (foundStart && end >= charIndex && end <= nextCharIndex) {
        range.setEnd(node, end - charIndex);
        stop = true;
      }
      charIndex = nextCharIndex;
    } else {
      i = node.childNodes.length;
      while (i--) {
        nodeStack.push(node.childNodes[i]);
      }
    }
  }
  sel = document.getSelection();
  sel.removeAllRanges();
  sel.addRange(range);
}