note
In React, function components are a simpler way to write components that only contain a render method and don’t have their own state. Instead of defining a class which extends React.Component, we can write a function that takes props as input and returns what should be rendered. Function components are less tedious to write than classes, and many components can be expressed this way.
The square class can be converted to:
function Square(props) { return ( <button className="square" onClick={props.onClick}> {props.value} </button> ); }