JSFiddle - React, Tailwind, and code Playground

HTML

<div id='sheet'>
<div class='item' id='field-18583'>This is yet another test</div>
<div class='item' id='field-18585'>This is test data</div>
</div>

JavaScript

var searchTerm = 'This is',
    replaceWith = 'This is new',
    updateObj = {};
$("#sheet div.item:contains('" + searchTerm + "')").each(function(){
   // use id to build an update object
    updateObj[this.id.replace('field-', '')] = {
        oldText: searchTerm, 
        newText: replaceWith
    }; // not sure what you are trying to save here
   // manipulate html
   this.innerHTML = this.innerHTML.replace(searchTerm, replaceWith);
});