- better way of handling props, mostly if you write components that might be used by other developers
- can restrict the types and values that you receive for your props
- Person receives four important props: click, name, age, changed
- there is an extra package that you can add for this
- cmd `npm install --save prop-types`
- provided by react team, allows us to check the type of our property
- import statement: `import PropTypes from 'prop-types';`
- used by going below the class definition
- `Person.propTypes = { click: PropTypes.func, name: PropTypes.string, age: PropTypes.number, changed: PropTypes.func };`