Working with Multiple State Values
When building anything but very simple web apps or UIs, you will need multiple state values. Maybe users can not only enter their email but also a username or their address. Maybe you also need to track some error state or save shopping cart items. Maybe users can click a “like” button whose state should be saved and reflected in the UI. There are many values that change frequently and whose changes should be reflected in the UI.
Consider this concrete scenario: you have a component that needs to manage both the value entered by a user into an email input field and the value that was inserted into a password field. Each value should be captured once a field loses focus.
Since you have two input fields that hold different values, you have two state values: the entered email and the entered password. Even though you might use both values together at some point (for example, to log a user in), the values are not provided simultaneously...
