Typescript 无法推断构造函数返回类型

Question

type ArrayBufferViewConstructor<T> = new (buffer: ArrayBufferLike, byteOffset?: number, byteLength?: number) => T;

function asView<V, C extends ArrayBufferViewConstructor<V>>(
    TypedArray: C,
    v: BufferSource,
    byteOffset?: number,
    byteLength?: number,
  ): V{
    return undefined as V
  }

let a = asView(Uint8Array, new Uint32Array)
a

 declare type ArrayBufferViewConstructor<T> = new (buffer: ArrayBufferLike, byteOffset?: number, byteLength?: number) => T; declare function asView<V, C extends ArrayBufferViewConstructor<V>>(TypedArray: C, v: BufferSource, byteOffset?: number, byteLength?: number): V; declare let a: unknown;

I expected a is Uint8Array , but got unknown

{ "compilerOptions": { "strict": true, "noImplicitAny": true, "strictNullChecks": true, "strictFunctionTypes": true, "strictPropertyInitialization": true, "strictBindCallApply": true, "noImplicitThis": true, "noImplicitReturns": true, "alwaysStrict": true, "esModuleInterop": true, "declaration": true, "experimentalDecorators": true, "emitDecoratorMetadata": true, "target": "ES2017", "jsx": "react", "module": "ESNext", "moduleResolution": "node" } }

Playground Link: Provided

How do define the type make return type is Uint8Array ?

Answer 1

Making use of the built-in InstanceType , there is no need for the generic parameter V . We just need to use it here, in the return type of the function:

): InstanceType<C> {

Playground