Controlled Components

Summary

Form inputs whose value is driven entirely by React state (`value` + `onChange`), making React the 'single source of truth' for the input's value.

• 1Convert an uncontrolled input (using a ref) into a controlled one.
• 2Notice how controlled inputs let you validate/transform input on every keystroke.
• 3Learn when uncontrolled inputs (with refs) are actually the simpler choice.