Select Text

selectText.js

function selectText(selection) {
  var range = selection.getRangeAt(0);
  function replaceRange(s, start, end, substitute) {
    return s.substring(0, start) + substitute + s.substring(end);
  }
  var text = selection.baseNode.textContent.substring(range.startOffset, range.endOffset);

  var mark = `<mark>${text}</mark>`;
  range.startContainer.parentElement.innerHTML = replaceRange(range.startContainer.textContent, range.startOffset, range.endOffset, mark);
}