Masto/app/javascript/mastodon/reducers/history.js

import { Map as ImmutableMap, List as ImmutableList, fromJS } from "immutable";

import { HISTORY_FETCH_REQUEST, HISTORY_FETCH_SUCCESS, HISTORY_FETCH_FAIL } from "mastodon/actions/history";

const initialHistory = ImmutableMap({
  loading: false,
  items: ImmutableList(),
});

const initialState = ImmutableMap();

export default function history(state = initialState, action) {
  switch(action.type) {
    case HISTORY_FETCH_REQUEST:
      return state.update(action.statusId, initialHistory, history => history.withMutations(map => {
        map.set("loading", true);
        map.set("items", ImmutableList());
      }));
    case HISTORY_FETCH_SUCCESS:
      return state.update(action.statusId, initialHistory, history => history.withMutations(map => {
        map.set("loading", false);
        map.set("items", fromJS(action.history.map((x, i) => ({ ...x, account: x.account.id, original: i === 0 })).reverse()));
      }));
    case HISTORY_FETCH_FAIL:
      return state.update(action.statusId, initialHistory, history => history.set("loading", false));
    default:
      return state;
  }
}