Example languages reducer in Redux

languages.ts

import {ADD_LANGUAGE} from "../actions";
import {INITIAL_STATE} from "./initial-state";
import {ILanguage} from "../interfaces/languages";

export function languages(state = INITIAL_STATE.languages, action):ILanguage[] {
    switch (action.type) {
        case ADD_LANGUAGE:
            return state.concat(Object.assign({}, action.language));
    }

    return state;
}