【Functional and Class Components】

　　The simplest way to define a component is to write a JavaScript function:

　　This function is a valid React component because it accepts a single "props" object argument with data and returns a React element. We call such components "functional" because they are literally JavaScript functions.

　　You can also use an ES6 class to define a component:

　　The above two components are equivalent from React‘s point of view.

参考：https://facebook.github.io/react/docs/components-and-props.html#functional-and-class-components

Functional and Class Components