typescript - ts 泛型引用问题？

Question

今天面试遇到一道题，想了很久也没有想出来

type Events = {  ready: void  error: Error  reconnecting: { attempt: number; delay: number }}type RedisClient = {  on<T extends keyof Events>(event: T, f: (arg: Events[T]) => void): void}let aa: RedisClient = 这里要怎么写aa.on('ready', () => {  console.log(12312)})

我是这样写的，但是报错了

let aa: RedisClient = {  on: function (event, f): void {    switch (event) {      case 'ready':        f()        break      case 'error':        f(new Error())        break      case 'reconnecting':        f({ attemp: 1, delay: 1 })        break      default:        break    }  }}

f（）的参数有问题，想请教一下大家应该如何写?

Answer 1

let aa: RedisClient = {    on(event, fn) {        const redis: Events = {            ready: undefined,            error: new Error('error massage'),            reconnecting: {                attempt: 3,                delay: 300            }        }        fn(redis[event])    }}

Answer 2

type Events = {    ready: void    error: Error    reconnecting: { attempt: number; delay: number }}type RedisClient = {    on<T extends keyof Events>(event: T, f: (arg: Events[T]) => void): void}let aa: RedisClient = {    on(event, f): void {        switch (event) {            case 'ready':                (f as ((arg: Events["ready"]) => void))();                break            case 'error':                (f as ((arg: Events["error"]) => void))(new Error())                break            case 'reconnecting':                (f as ((arg: Events["reconnecting"]) => void))({ attempt: 1, delay: 1 })                break            default:                break        }    }}aa.on('ready', () => {    console.log(12312)})

只能这么写了

Answer 3

type RedisClient<T extends keyof Events> = {  on(event: T, f: (arg: Events[T]) => void): void}

只能这样改了，不然就只能强行as

Answer 4

type Events = {  ready: void  error: Error  reconnecting: { attempt: number; delay: number }}type RedisClient = {  on<T extends keyof Events>(event: T, f: (arg: Events[T]) => void): void}let aa: RedisClient = {  on: function<T extends keyof Events> (event: T, f: (arg: Events[T]) => void): void {    switch (event) {      case 'ready':        f(undefined as Events[T]); // 无参数        break;      case 'error':        f(new Error() as Events[T]); // Error参数        break;      case 'reconnecting':        f({ attempt: 1, delay: 1 } as Events[T]); // 对象参数        break;      default:        break;    }  }}aa.on('ready', () => {  console.log('Ready event')})aa.on('error', (e: Error) => {  console.log('Error event', e)})aa.on('reconnecting', (arg: { attempt: number; delay: number }) => {  console.log('Reconnecting event', arg.attempt, arg.delay)})