React Native. What does this declaration Component and function (data: Object): {[name: string]: number} {} mean?

Question

React Native

I opened someone else's Js code in the React Native project and saw such a function declaration there.
How many searched did not find an explanation.
1)
When creating a pure React project.

type Props = {};
export default class App extends Component<Props> {
  render() {
    return (
      <View style={styles.container}>
        <Text style={styles.welcome}>
          Welcome to React Native!
        </Text>
        <Text style={styles.instructions}>
          To get started, edit App.js
        </Text>
        <Text style={styles.instructions}>
          {instructions}
        </Text>
      </View>
    );
  }
}

By what rules does type Props = {}; ?
Why Component
2 is needed)

export function create(data: Object): {[name: string]: number} {}

How does it work and most importantly where can I read about it?

Answer 1

It's not just JavaScript, but TypeScript or Flow.

type props = {}

is a type alias. More details in the documentation: www.typescriptlang.org/docs/handbook/advanced-type... or https://flow.org/en/docs/types/aliases/
Regarding the use of the component, yes, you are right, in this In this case, it was preferable to use a pure function, because the component is stateless. Probably, the author assumed that in the future there would be stateful and used the class.