How to make (+) sign stop working after max availability is reached.

I already set the quantity per variant, but customers can click click higher than the available quantity. They cannot add the item their carts if they exceed the available number, but have no way of knowing how many are actually available until they keep decreasing the number until the item goes through. How do I fix it so that customers can immediately see that they’ve reached the maximum availability of a variant (or the + button should stop working/raising the quantity)? TIA.