es6 代码片段理解

代码片段理解：

 [INCREMENT]: (state, action) => {
     const { payload: { id } } = action

     //because payload contains the id and we already know that we are about
     //to increment the value of that id, we modify only that value by one

     return {
       ...state,
       counters: {
         ...state.counters,
         [id]: state.counters[id] + 1
       }
     }
   },

line 2:

const { payload: { id } } = action
相当于： id = action.payload.id

line 8 - 10:

{
 8       ...state,
 9       counters: {
10         ...state.counters,
11         [id]: state.counters[id] + 1
12       }
13     }

是表达：state.counter[id] =  state.counters[id] + 1