JSFiddle - React, Tailwind, and code Playground

HTML

<div contenteditable="true">this is your text</div>

<button onclick="window.mark()">
Add markers
</button>

JavaScript

var markerHTML = '&#x200b;';

window.mark = function() {
  var range = document.getSelection().getRangeAt(0);

  range2 = range.cloneRange();
  var marker = document.createElement('span');
  marker.id="selection-marker-1";
  marker.className="redactor-selection-marker";
  marker.innerHTML = markerHTML;  
  
  var marker2 = document.createElement('span');
  marker2.id="selection-marker-2";
  marker2.className="redactor-selection-marker";
  marker2.innerHTML = markerHTML;  
  
  range2.collapse(true);
  range2.insertNode(marker);
  
  range3 = range.cloneRange();
  range3.collapse(false);
  range3.insertNode(marker2);
  
  range.setStart(document.getElementById('selection-marker-1'), 0);
  range.setEnd(document.getElementById('selection-marker-2'), 0);
  
  marker.parentNode.removeChild(marker);
  marker2.parentNode.removeChild(marker2);
    
  range2 = range.cloneRange();
  var marker = document.createElement('span');
  marker.id="selection-marker-1";
  marker.className="redactor-selection-marker";
  marker.innerHTML = markerHTML;  
  
  var marker2 = document.createElement('span');
  marker2.id="selection-marker-2";
  marker2.className="redactor-selection-marker";
  marker2.innerHTML = markerHTML;  
  
  range2.collapse(true);
  range2.insertNode(marker);
  
  range3 = range.cloneRange();
  range3.collapse(false);
  range3.insertNode(marker2);
  
  document.execCommand('strikethrough');
}