A function called DeepClone.js which takes an object and creates a copy of it. Tested using jest (see DeepClone.test.js)

DeepClone.js

const DeepClone = (obj) => {
    let copy;

    // Handle the 3 simple types, and null or undefined
    if (null === obj || "object" !== typeof obj) return obj;

    // Handle Date
    if (obj instanceof Date) {
        copy = new Date();
        //  A way to make one Date the same as another is by calling the setTime method
        copy.setTime(obj.getTime());
        return copy;
    }

    // Handle Array
    if (obj instanceof Array) {
        copy = [];
        for  (let i = 0; i < obj.length; ++i) {
            copy[i] = DeepClone(obj[i]);
        }
        return copy;
    }

    // Handle Object
    if (obj instanceof Object) {
        copy = {};
        for (let attr in obj) {
            if (obj.hasOwnProperty(attr)) copy[attr] = DeepClone(obj[attr]);
        }
        return copy;
    }

    throw new Error("Unable to copy obj! Its type isn't supported.");
}

module.exports = {DeepClone};

DeepClone.test.js

/**
 * Used to test DeepClone.js
 */

const { DeepClone } = require('./DeepClone')

const obj = {name: "Paddy", address: {town: "Lerum", country: "Sweden"}};

test("cloning an object", () => {
	// toEqual compares the values of two objects. 
	// it checks the equality of all the properties or elements. 
	// It does not compare references
	expect(DeepClone(obj)).toEqual(obj)
})