我想实现一个emitEvent(event, extra?)
函数,该函数将受到已知字符串的字符串文字枚举的约束,例如POPUP_OPEN
,POPUP_CLOSED
等。此函数接受第二个参数,该参数也是一个显式定义的字典形状,只能与特定的事件键一起使用。
这是所有已知事件的字典:
interface Events {
POPUP_OPEN: {name:'POPUP_OPEN',extra: {count:number}},
POPUP_CLOSED: {name:'POPUP_CLOSED'},
AD_BLOCKER_ON: {name:'AD_BLOCKER_ON', extra: {serviceName:string}},
AD_BLOCKER_OFF: {name:'AD_BLOCKER_OFF'}
}
具有要求的类型约束的用法:
// $ExpectType {object: string; action: string; value: string;}
const t1 = emitEvent('POPUP_CLOSED')
// $ExpectError -> no extra argument allowed
const t11 = emitEvent('POPUP_CLOSED', {what:'bad'})
// $ExpectType {object: string;action: string;foo: string; count: number;}
const t2 = emitEvent('POPUP_OPEN',{count: 1231})
// $ExpectError -> extra argument is missing
const t22 = emitEvent('POPUP_OPEN')
我的实现:
此实现存在一个大问题,因为字典值已定义extra
,未定义时TS不会抱怨
// ✅ NO ERROR
const t2 = emitEvent('POPUP_OPEN',{count: 1231})
// ✅ Error
const t2 = emitEvent('POPUP_OPEN',{})
// ?NO ERROR -> THIS SHOULD ERROR !
const t2 = emitEvent('POPUP_OPEN')
实施:
type ParsedEvent<Extra = void> = Extra extends object ? BaseParsedEvents & Extra : BaseParsedEvents
type BaseParsedEvents = {
object:string
action:string
value:string
}
type KnownEvents = keyof Events
type GetExtras<T> = T extends {name: infer N, extra: infer E} ? E : never;
function emitEvent<T extends KnownEvents>(event:T): ParsedEvent
function emitEvent<T extends KnownEvents, E extends GetExtras<Events[T]>>(event:T, extra: E): ParsedEvent<E>
function emitEvent<T extends string, E extends object>(event:T, extra?: E) {
const parsedEmit = parse(event)
return {...parsedEmit,...extra}
}
function parse(event:string): BaseParsedEvents {
const [object,action,value] = event.split('_')
return {object,action,value}
}
总的来说,这恐怕无法实现,但希望我错了:)
答案 0 :(得分:1)
您可以使用tuples in rest parameters而不是重载来使函数接受可变数量的参数。 GetExtras
将返回带有单个E
元素的元组或空的元组。然后,我们可以将GetExtras
扩展为函数的扩展参数:
interface Events {
POPUP_OPEN: {name:'POPUP_OPEN',extra: {count:number}},
POPUP_CLOSED: {name:'POPUP_CLOSED'},
AD_BLOCKER_ON: {name:'AD_BLOCKER_ON', extra: {serviceName:string}},
AD_BLOCKER_OFF: {name:'AD_BLOCKER_OFF'}
}
// $ExpectType {object: string; action: string; value: string;}
const t1 = emitEvent('POPUP_CLOSED')
// ✅ NO ERROR
const t21 = emitEvent('POPUP_OPEN',{count: 1231})
// ✅ Error
const t213 = emitEvent('POPUP_OPEN',{})
// ✅ ERROR as expected
const t223 = emitEvent('POPUP_OPEN')
type ParsedEvent<Extra extends [object] | [] = []> = Extra extends [infer E] ? BaseParsedEvents & E : BaseParsedEvents
type BaseParsedEvents = {
object:string
action:string
value:string
}
type KnownEvents = keyof Events
type GetExtras<T> = T extends {name: infer N, extra: infer E} ? [E] : [];
function emitEvent<T extends KnownEvents, E extends GetExtras<Events[T]>>(event:T, ...extra: E): ParsedEvent<E>
function emitEvent<T extends string, E extends object>(event:T, extra?: E) {
const parsedEmit = parse(event)
return {...parsedEmit,...extra}
}
function parse(event:string): BaseParsedEvents {
const [object,action,value] = event.split('_')
return {object,action,value}
}
答案 1 :(得分:1)
如何将您的第一个函数重载声明限制为不包含extra
属性的事件?
// define events, that do not have extra property
// "POPUP_CLOSED" | "AD_BLOCKER_OFF"
type KnownEventsWithoutExtra = {
[K in keyof Events]: Events[K] extends { name: string; extra: object }
? never
: K
}[keyof Events];
// single argument overload is restricted to above events
function emitEvent<T extends KnownEventsWithoutExtra>(event: T): ParsedEvent;
// will error now
const t4 = emitEvent("POPUP_OPEN");