cloning objects in javascript

clonetest.ts

function cloneObject(obj: any): any {
    switch (obj["constructor"]) {
        case Date: return new Date(obj);
        case Object: return Object.keys(obj).reduce<{ [key: string]: any }>((newObj, key) => (newObj[key] = cloneObject(obj[key]), newObj), {});
        case Array: return obj.map(cloneObject);
    }
    return obj;
}

// Test
const obj = { number: 100, string: "string", boolean: true, object: { key: "value" }, date: new Date(), array: [0] },
    objClone = { ...obj }, // spread operator does not copy inner reference keys that hold reference types like object, array, date so are not fully cloned
    objClone2 = cloneObject(obj);
// Update obj
obj.number += 1, obj.string += "1", obj.boolean = false, obj.object.key += "1", obj.date.setHours(0), obj.array.push(1);
// Print
console.log(objClone, objClone2);
/** The output here is of variable objClone, which is spread of obj. The reference types of the new object are modified when we modify obj.
{
    number: 100, string: 'string', boolean: true,
    object: { key: 'value1' }, // <<< object also updated as this is by reference
    date: 2021-03-27T18:50:02:0222, // <<< date also updated as this is by reference
    array: [ 0, 1 ] // <<< array also updated as this is by reference
}
{
    number: 100, string: 'string', boolean: true,
    object: { key: 'value' },
    date: 2021-03-28T13:15:16:0222,
    array: [ 0 ]
}
*/