JSFiddle - React, Tailwind, and code Playground

HTML

<p>
In arr :
<span id="testarr">
</span></p>
<p>
In clone :
<span id="testclone">
</span>
</p>
<script
  src="https://code.jquery.com/jquery-3.2.1.min.js"
  integrity="sha256-hwg4gsxgFZhOsEEamdOYGBf13FyQuiTwlAQgxVSNgt4="
  crossorigin="anonymous"></script>

JavaScript

var arr = [{'obj1':1}, {'obj2':2}];
var clone = arr.slice(0);
clone[0].test = "defined";
$("#testarr").html(arr[0].test);
$("#testclone").html(clone[0].test);