JSFiddle - React, Tailwind, and code Playground

JavaScript

function Custom() {
    this.prop = 'before';
};

var original = { custom: new Custom() };
var copy = $.extend(true, {}, original);

console.log(original, copy);

copy.custom.prop = 'after'; // changing the copy should not affect the original
console.log((original.custom.prop === 'before' && 'PASS') || 'FAIL');