vuex报错: [vuex] Expects string as the type, but found undefined.

报错如图

检查了好久，发现

import * as types from '../mutation-types'
const actions = {
  add({commit}){
    commit(types.ADD)
  }
}
const mutations = {
  [types.ADD](state){
    state.count++
  }
}

这里的 [types.ADD] 如果换成

const actions = {
  add({commit}){
    commit('ad')
  }
}
const mutations = {
  ad(state){
    state.count++
  }
}

就不会报错

判断结果：[types.ADD]这里有问题，

于是 检查mutation-types.js文件

原来是ADD等号右边没有加引号的缘故。导致[types.ADD]的出错