[英]Extensible, strongly typed Event Emitter Interface in Typescript
我在Typescript中使用強類型事件發射器接口已有一段時間了,但是現在我需要它來支持向其添加自己的事件的子類。 在某些時候,Typescript無法識別基類事件。
以下是壓縮版本中的代碼( Playground Link ):
type UnionToIntersection<U> =
(U extends any ? (k: U) => void : never) extends ((k: infer I) => void) ? I : never;
type AddParameters<ListenersT, EventT> =
ListenersT extends (...args: infer ArgsT) => void
? (event: EventT, ...args: ArgsT) => Promise<boolean>
: never;
type EmitSignatures<ListenersT> =
{ [EventT in keyof ListenersT]: AddParameters<ListenersT[EventT], EventT> };
type EmitAll<ListenersT> = UnionToIntersection<EmitSignatures<ListenersT>[keyof ListenersT]>
type OnSignatures<ListenersT, ReturnT> =
{ [EventT in keyof ListenersT]: (event: EventT, listener: ListenersT[EventT]) => ReturnT };
type OnAll<ListenersT, ReturnT> =
UnionToIntersection<OnSignatures<ListenersT, ReturnT>[keyof ListenersT]>;
type EventEmitter<ListenersT> = EmitterInterface<ListenersT>;
export interface EmitterInterface<ListenersT>
{
emit: EmitAll<ListenersT>;
on: OnAll<ListenersT, this>;
}
/////////////////////////////////////////////////////////////////////////////////////////////
interface VehicleEvents
{
accelerate(acceleration: number): void;
brake(deceleration: number): void;
}
interface BusEvents extends VehicleEvents
{
doorStateChange(front: boolean, middle: boolean, rear: boolean): void
}
interface Vehicle<E extends VehicleEvents> extends EventEmitter<E>
{
onSig: OnSignatures<E, this>;
onSigs: OnSignatures<E, this>[keyof E];
}
class Vehicle<E extends VehicleEvents>
{
public constructor()
{ this.on('brake', () => this.flashBrakeLights()); } // supposed to work?
public flashBrakeLights(): void {}
public hitTheGas(strength: number): void
{ this.emit('accelerate', strength * 42); } // supposed to work?
public test(): void
{
this.onSig.accelerate;
this.onSig.brake;
this.onSigs('accelerate', (a) => undefined); // error I don't understand
this.onSigs('brake', (d) => undefined); // error I don't understand
this.onSigs('foo', () => undefined); // supposed to error
}
}
interface Bus extends EventEmitter<BusEvents> {}
class Bus extends Vehicle<BusEvents>
{
public doorState: [boolean, boolean, boolean] = [false, false, false];
public constructor()
{
super();
this.on('accelerate', () => {
this.door(0, false);
this.door(1, false);
this.door(2, false);
});
}
public door(index: number, state: boolean): void
{
this.doorState[index] = state;
this.emit('doorStateChange', ...this.doorState);
}
}
export const bus = new Bus();
E
類型被聲明為VehicleEvents
擴展,應該足以讓Typescript知道存在accelerate
和brake
事件,不是嗎?
為什么這不起作用的任何解釋? 關於如何解決此問題或以其他方式實現我所需要的任何想法?
問題在於,如果類中仍然包含未解析的類型參數,則無法解析那些花哨的條件類型(不確定它們來自cough的來源 )。 因此,盡管使用通用類型參數進行可擴展性的方法似乎是一個好主意,但其效果是,它使類內部的對象無法emit
on
並且在類內部emit
不可用的信息。
一種解決方案是不使用類型參數,而僅使用事件接口本身。 的問題(無疑是您發現的)是,它使類無法擴展,因為on
和emit
任何派生版本都不與基本類型版本兼容。
為了解決這個問題,我們可以使用一個從基本類型on
移除並emit
的函數。 這有點駭人聽聞,但我認為沒有更好的方法。
interface VehicleEvents {
accelerate(acceleration: number): void;
brake(deceleration: number): void;
}
interface BusEvents extends VehicleEvents {
doorStateChange(front: boolean, middle: boolean, rear: boolean): void
}
interface Vehicle extends EventEmitter<VehicleEvents> {}
class Vehicle {
public constructor() {
this.on('brake', () => this.flashBrakeLights()); //ok
}
public flashBrakeLights(): void { }
public hitTheGas(strength: number): void { this.emit('accelerate', strength * 42); } // ok
}
type Omit<T, K extends keyof any> = Pick<T, Exclude<keyof T, K>>
interface Bus extends EventEmitter<BusEvents> { }
function extendEmitter<TBaseCtor extends new (...a: any[])=> any>(ctor: TBaseCtor){
return ctor as (new (...a: ConstructorParameters<TBaseCtor>) => Omit<InstanceType<TBaseCtor>, 'on' | 'emit'>)
}
class Bus extends extendEmitter(Vehicle) {
public doorState: [boolean, boolean, boolean] = [false, false, false];
public constructor() {
super();
this.on('accelerate', () => {
this.door(0, false);
this.door(1, false);
this.door(2, false);
});
}
public door(index: number, state: boolean): void {
this.doorState[index] = state;
this.emit('doorStateChange', ...this.doorState);
}
}
export const bus = new Bus();
上面的版本不能確保新派生的對象正確地實現了基本事件。 我們可以編寫一個版本來驗證這一點,但需要對原始定義進行一些改動,以允許我們從基本類型中提取事件接口:
type UnionToIntersection<U> =
(U extends any ? (k: U) => void : never) extends ((k: infer I) => void) ? I : never;
type AddParameters<ListenersT, EventT> =
ListenersT extends (...args: infer ArgsT) => void
? (event: EventT, ...args: ArgsT) => Promise<boolean>
: never;
type EmitSignatures<ListenersT> =
{ [EventT in keyof ListenersT]: AddParameters<ListenersT[EventT], EventT> };
type EmitAll<ListenersT> = UnionToIntersection<EmitSignatures<ListenersT>[keyof ListenersT]>
type OnSignatures<ListenersT, ReturnT> =
{ [EventT in keyof ListenersT]: (event: EventT, listener: ListenersT[EventT]) => ReturnT };
type OnAll<ListenersT, ReturnT> =
UnionToIntersection<OnSignatures<ListenersT, ReturnT>[keyof ListenersT]>;
type EventEmitter<ListenersT> = EmitterInterface<ListenersT>;
export interface EmitterInterface<ListenersT>
{
emit: EmitAll<ListenersT>;
on: OnAll<ListenersT, this> & {__source: ListenersT}; // do not use __source, just here to allow EventTypes to work
}
type EventTypes<T> = T extends EventEmitter<infer U> ? U : never;
/////////////////////////////////////////////////////////////////////////////////////////////
interface VehicleEvents {
accelerate(acceleration: number): void;
brake(deceleration: number): void;
}
interface BusEvents extends VehicleEvents {
doorStateChange(front: boolean, middle: boolean, rear: boolean): void
}
interface Vehicle extends EventEmitter<VehicleEvents> {}
class Vehicle {
public constructor() {
this.on('brake', () => this.flashBrakeLights()); //ok
}
public flashBrakeLights(): void { }
public hitTheGas(strength: number): void { this.emit('accelerate', strength * 42); } // ok
}
type Omit<T, K extends keyof any> = Pick<T, Exclude<keyof T, K>>
interface Bus extends EventEmitter<BusEvents> { }
function extendEmitter<TBaseCtor extends new (...a: any[])=> any>(ctor: TBaseCtor){
return function<TEvents extends EventTypes<InstanceType<TBaseCtor>>>(){
return ctor as (new (...a: ConstructorParameters<TBaseCtor>) => Omit<InstanceType<TBaseCtor>, 'on' | 'emit'> & EventEmitter<TEvents>)
}
}
class Bus extends extendEmitter(Vehicle)<BusEvents>() {
public doorState: [boolean, boolean, boolean] = [false, false, false];
public constructor() {
super();
this.on('accelerate', () => {
this.door(0, false);
this.door(1, false);
this.door(2, false);
});
}
public door(index: number, state: boolean): void {
this.doorState[index] = state;
this.emit('doorStateChange', ...this.doorState);
}
}
export const bus = new Bus();
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