Function components have props object which contains values passed to the component via props/attributes, and they don't have render or lifecycle methods.
This is the reason why they are called "functional stateless components".
Function components return a JSX string.
Class components have state and props.
Class components have render() method which renders the JSX.
The state is an object defined inside of the React class component.
React class components have React's built-in method setState() we must use to update the state.
React's built-in setState() method triggers re-rendering of the DOM when state is changed.
Only the class component itself can define the state (object) or change it's existing state through this.setState().