Is an object inside an array passed by reference?

Question

So let's say we have an array of objects like this:

let cards = [
    {
        suit: 'spades',
        "value": '10'
    },
    {
        suit: 'hearts',
        value: 'Q'
    },
    {
        suit: 'clubs',
        value: '5'
    }
]

Now to shuffle it, I saw a function like this:

function shuffle(cards) {
    for (let i = cards.length - 1; i > 0; i --) {
        const newIndex = Math.floor(Math.random() * (i + 1));
        const oldValue = cards[newIndex];   // cards[newIndex] is an object, and we're assigning its address to oldValue
        cards[newIndex] = cards[i];         // Now we're changing cards[newIndex] address to an address of another object
                                            // So the oldValue address we set one line higher should change too 
                                            // Yet it stays unchanged
    }
}

The thing I don't understand is described in the comments of the code above.

I wanted to ask, why it behaves like this - isn't it a classical 'pass by reference' example? Why is the oldValue variable not changing after we change the address of the object passed to it?

Answer 1

You are assigning new value to cards[newIndex]. The rule about reference is not valid here as now cards[newIndex] points to something else only(different address in memory). The original variable still exists at a different address. Hence oldValue still points to the, well, old value.

If you would have made any modifications to cards[newIndex] like: cards[newIndex]['value'] = 9; it would have reflected.