详解vuex中action何时完成以及如何正确调用dispatch的思考

 dispatch (_type, _payload) {
 // check object-style dispatch
 const {
 type,
 payload
 } = unifyObjectStyle(_type, _payload)

 const action = { type, payload }
 const entry = this._actions[type]
 if (!entry) {
 if (process.env.NODE_ENV !== 'production') {
 console.error(`[vuex] unknown action type: ${type}`)
 }
 return
 }

 try {
 this._actionSubscribers
 .filter(sub => sub.before)
 .forEach(sub => sub.before(action, this.state))
 } catch (e) {
 if (process.env.NODE_ENV !== 'production') {
 console.warn(`[vuex] error in before action subscribers: `)
 console.error(e)
 }
 }

 const result = entry.length > 1
 ? Promise.all(entry.map(handler => handler(payload)))
 : entry[0](payload)

 return result.then(res => {
 try {
 this._actionSubscribers
 .filter(sub => sub.after)
 .forEach(sub => sub.after(action, this.state))
 } catch (e) {
 if (process.env.NODE_ENV !== 'production') {
 console.warn(`[vuex] error in after action subscribers: `)
 console.error(e)
 }
 }
 return res
 })
 }