jira desc history diff - quick hack

history-diff.js

var hItems = document.querySelectorAll("div[data-testid='issue-history.ui.history-items.generic-history-item.history-item']") 
var desc = hItems[1]
if (hItems.length < 1) {
  alert("switch to history tab and re-run")
  return
}
else {
  Array.from(hItems).forEach(function (desc, idx){
    if (desc.childNodes.length > 1 ){
      prof = desc.childNodes[0]
      descAction = desc.childNodes[1]
      descActionText =  descAction.childNodes[0].innerText
    
      descDiff = descAction.childNodes[1]
      var oldDesc
      var newDesc
    
      if (descDiff.childNodes.length > 2) {
        oldDesc = descDiff.childNodes[0]
        newDesc = descDiff.childNodes[2]
      }
      
      var strDesc = 'updated the Description'
      
      if (descActionText.includes(strDesc)) {
        var diffBtn = document.createElement('button');
        diffBtn.textContent = 'Diff!';
        
        diffBtn.addEventListener('click', () => {
          diffThis(idx, descDiff, oldDesc, newDesc)
        });
        
        prof.appendChild(diffBtn)
      }
    }
  })
  
  
  function injectJS(url) {
    var po = document.createElement('script');
    po.type = 'text/javascript';
    po.async = true;
    po.src = url;
    var s = document.getElementsByTagName('script')[0];
    s.parentNode.insertBefore(po, s);
  }
  injectJS('https://cdnjs.cloudflare.com/ajax/libs/jsdiff/5.2.0/diff.min.js');
  
  function diffThis(idx, container, left, right) {
    // console.log(idx, container, left, right)
  
    var diffDiv = document.createElement('div');
    // diffDiv.style.whiteSpace = 'break-spaces'
    left.parentElement.parentElement.appendChild(diffDiv)
  
    var diffedText = ""

    const diff = Diff.diffWords(left.textContent, right.textContent),
      display = diffDiv,
      fragment = document.createDocumentFragment();
      diff.forEach((part) => {
        if (part.added) {
            diffedText += '{color:#36b37e}' + part.value + '{color}'
        }
        else if (part.removed) {
            diffedText += '{color:#ff5630}' + part.value + '{color}'
        }
        else {
            diffedText += '{color:#97a0af}' + part.value + '{color}'
        }
      });

    
    //   console.log(diffedText)

      jQuery.ajax({
        contentType: 'application/json',
        type: 'POST',
        url: '/rest/api/1.0/render',
        data: '{"rendererType":"atlassian-wiki-renderer","unrenderedMarkup":' + JSON.stringify(diffedText) +',"issueKey":"SUPPORT-1"}',
        success: function( response ) {
            console.log(response);
            display.innerHTML = response
        }
    });
  }
}

using https://github.com/kpdecker/jsdiff