How to type Redux actions and Redux reducers in TypeScript?

Question

What is the best way to cast the action parameter in a redux reducer with typescript? There will be multiple action interfaces that can occur that all extend a

Answer 1

I might be late to the dance but enum's FTW!

enum ActionTypes {
  A: 'ANYTHING_HERE_A',
  B: 'ANYTHING_HERE_B',
}

interface IActionA {
  type: ActionTypes.A;
  a: string;
}

interface IActionB {
  type: ActionTypes.B;
  b: string;
}

type IAction = IActionA | IActionB

const reducer = (action: IAction) {
  switch (action.type) {
    case ActionTypes.A:
      return console.info('action a: ', action.a)

    case ActionTypes.B:
      return console.info('action b: ', action.b)
    }
}