要求：顺次执行fetch1=>fetch2=>fetch3，先执行fetch1，须要将fetch1的后果作为fetch2的参数，fetch2的后果作为fetch3的参数。
interface IEvents { [key: string]: Array<Function>}class EventListener { events: IEvents constructor() { this.events = {} } listen(key, fn) { let fns = this.events[key]; if (fns) { fns.push(fn) } else { this.events[key] = [fn] } } on(key, payload) { const fns = this.events[key] if (fns && fns.length > 0) { const fn = fns.shift() fn(payload) } } remove(key, fn) { const fns = this.events[key] if (!Array.isArray(fns)) return const index = fns.indexOf(fn) if (index !== -1) { fns.splice(index, 1) } }}let listener = new EventListener()const fetch1 = () => { setTimeout(() => { const res = { current: 'fetch1', next: 'fetch2' } console.log(res) listener.on('fetch2', res) })}const fetch2 = (payload) => { setTimeout(() => { const res = { current: payload.next, next: 'fetch3' } console.log(res) listener.on('fetch3', res) })}const fetch3 = (payload) => { console.log({ current: payload.next, next: '' })}listener.listen('fetch2', fetch2)listener.listen('fetch3', fetch3)fetch1()