InputEvent.inputType

var aString = inputEvent.inputType;

<p id="log">Input type: </p>
<div contenteditable="true" style="margin: 20px;padding: 20px;border:2px dashed red;">
  <p>Some sample text. Try inserting line breaks, or deleting text in different ways, or pasting different content in.</p>
  <hr>
  <ul>
    <li>A sample</li>
    <li>bulleted</li>
    <li>list.</li>
  </ul>
  <p>Another paragraph.</p>
</div>

const log = document.getElementById('log');
const editable = document.querySelector('div[contenteditable]');
editable.addEventListener('input', logInputType);

function logInputType(event) {
  log.textContent = `Input type: ${event.inputType}`;
}