<script src="https://unpkg.com/react@17.0.2/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@17.0.2/umd/react-dom.development.js"></script>
<script src="https://cdn.jsdelivr.net/npm/@babel/standalone@7.14.6/babel.min.js"></script>
<script type="text/babel">
const array1 = [1, 2, 3];
const array2 = [4, 5, 6];
const concatenatedArray = [...array1, ...array2];
<h1>React Js Concat Array using Spread Operator</h1>
<p>concatenatedArray : {concatenatedArray}</p> ReactDOM.render(<App />, document.getElementById("app"));