ref

In Vue, ref is a simple reactive data wrapper used to make an ordinary JavaScript value reactive. It has only one key, which is value, and it is used to store the wrapped value.

Since ref has only one key, it requires only one dependency(dep) to track the dependencies related to this key.

When the value of ref changed, this dep notifies the relevant observers, which triggers updates to the views associated with the ref or performs other side effects.

Therefore, for a ref, only one dep is needed to manage its dependencies and ensure that it triggers updates or side effects correctly.