Equivalent for `handleActions` from the redux-actions` library.

create-reducer.ts

import { AnyAction, Reducer } from 'redux';

/**
 * Equivalent for `handleActions` from the redux-actions` library.
 * @see https://redux.js.org/recipes/reducing-boilerplate#generating-reducers
 *
 * @template T Reducer shape.
 */
export function createReducer<T>(handlers: Record<string, Reducer<T>>, initialState: T): Reducer<T> {
  return (state: T = initialState, action: AnyAction): T => {
    if (action.type in handlers) {
      return handlers[action.type](state, action);
    }

    return state;
  };
}