CODEWITHSUNDEEP
javascriptreactjsecmascript-6es6-class
hackrnaut
hackrnaut

Reputation: 583

What does <> next to extends class does in JS?

In facebooks flux-utils example, they do something like this:

import {ReduceStore} from 'flux/utils';

class CounterStore extends ReduceStore<number> {
  getInitialState(): number {
    return 0;
  }

  reduce(state: number, action: Object): number {
    switch (action.type) {
      case 'increment':
        return state + 1;

      case 'square':
        return state * state;

      default:
        return state;
    }
  }
}

Can anyone tell me what the <number> angle brackets next to ReduceStore does in JS?

I tried to look this up but don't really know what this es6 feature is called...

Thanks to anyone that helps!

Upvotes: 0

Views: 91

Answers (1)

Andrew Li
Andrew Li

Reputation: 57954

It isn't an ES6 feature, it's part of Flow, a static typechecker for your ES6 code. It's sort of like TypeScript in the sense it adds new syntax though they have their substantial differences (TypeScript is full-fledged language). Flow uses Babel to transpile your type annotations to pure ES6.

Upvotes: 5

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