What does es6 new grammar mean

  node.js, question
import { handleActions } from 'redux-actions';
 import { combineReducer } from 'redux';
 
 const todos = handleActions({
 
 ['todos/get'](state) {
 return { ...state, loading: true, };
 },
 //What does this passage mean ['todos/get'](state){}, es6 new syntax?
 ['todos/get/success'](state, action) {
 return { ...state, list: action.payload, loading: false, };
 },
 ['todos/get/failed'](state, action) {
 return { ...state, err: action.err, loading: false, };
 },
 ['todos/delete'](state, action) {
 const id = action.payload;
 const newList = state.list.filter(todo => todo.id !  == id);
 return { ...state, list: newList, };
 },
 ['todos/create'](state, action) {
 const text = action.payload;
 const newTodo = { text, };
 return { ...state, list: [newTodo, ...state.list], };
 },
 ['todos/toggleComplete'](state, action) {
 const id = action.payload;
 const newList = state.list.map(todo => {
 if (id === todo.id) {
 return { ...todo, isComplete: !  todo.isComplete };
 } else {
 return todo;
 bracket
 });
 return { ...state, list: newList, };
 },
 ['todos/toggleCompleteAll'](state, action) {
 const isComplete = action.payload;
 const newList = state.list.map(todo => ({ ...todo, isComplete }));
 return { ...state, list: newList, };
 },
 }, {
 list: [],
 loading: false,
 });
 
 export default todos;

It should be a way to define routes.