JSFiddle - React, Tailwind, and code Playground

HTML

<div contenteditable="true" id="editor">
        <p>This is example text with <span class="spoiler">spoiler<strong>s</strong></span></p>
      <p>The <span class="spoiler">spoiler</span> exists in multiple paragraphs</p>
    </div>
    <button onclick="removeSpoiler();">remove spoiler</button>

JavaScript

function removeSpoiler(){
        var selection = window.getSelection();
        if (selection.rangeCount) {
            var range = selection.getRangeAt(0);
            // ??
        }
    }