JSFiddle - React, Tailwind, and code Playground

JavaScript

var arr = {
        title: "Obect",
        elements: [
            { id: 1, title: "Element 1" },
            { id: 2, title: "Element 2" }
        ]
    };

function processElement(item) {
    item = { id: 999, title: "New Item" };
}

processElement(arr.elements[1]);
console.log(arr);