ngrx-reducer.ts

import { createAction, createReducer, on, props } from "@ngrx/store";

const add = createAction("[Todos] Add", props<{ text: string }>());
const reset = createAction("[Todos] Reset");

type Todo = {
  done: boolean;
  text: string;
};
const initialState = {
  todos: [] as Todo[]
};

const reducer = createReducer(
  initialState,
  on(add, (state, { text }) => ({
    todos: [
      ...state.todos,
      {
        done: false,
        text
      }
    ]
  })),
  on(reset, () => initialState)
);