Question

我正在编写通用方法以便在不同的前端应用程序中使用它们，其想法是能够调用函数.postAsync<CustomModel>('www.mysite.com',..., CustomModel);，预期的响应是CustomModel对象。

我希望能够为第二个参数设置默认值，以便默认情况下该值将是一个不同的模型，并且可以在需要时覆盖。

如何为类型Constructable<T>的自变量设置默认值，其中接口Constructable表示

interface Constructable<T> { new(params : any): T ;}

我尝试设置一个带参数的接口的默认值并将该参数设置为不同的类型，但是我总是收到错误Type Constructable<CustomModel> is not assignable to type Constructable<T>。我还在CustomModel的通用方法中设置了T的默认类型，然后尝试了此操作并得到了相同的错误。

interface Constructable<T> { new(params : any): T ;}


export default class WebapiBase {

    static async postAsync<T = CustomModel>(
        uri: string,
        body: object,
        headers: CustomHeaders = new CustomHeaders(),
        // This is the part giving errors
        model: Constructable<T> = <Constructable<CustomModel>>,): Promise<T> {
        return this.requestAsync<T>(model, HTTP_METHOD.POST, uri, headers, body);
    }

    private static async requestAsync<T>(
        model: Constructable<T>,
        method: HTTP_METHOD,
        uri: string,
        headers: CustomHeaders,
        body?: object): Promise<T> {
        const url = new URL(uri, window.location.origin);
        const request = this.buildRequest(url, method, headers, body);
        const bodyResponse = await fetch(request)
            .then(response => this.validate(response, request.headers))
            .then(validResponse => this.extractBody(validResponse))
            // Here is where the response body is being used to initialise one of the custom models that we are passing in. Code below
            .then(extractedBody => this.buildModel<T>(model, extractedBody))
            .catch((error) => { throw this.handleError(error); });
        return bodyResponse;
    }

    private static buildModel<T>(
        Model: Constructable<T>,
        params: ResponseBody,
    ): T {
        return new Model(params);
    }
}

我希望我不必将模型传递给方法postAsync()，并且它总是会返回CustomModel对象。但实际上我收到此错误Type Constructable<CustomModel> is not assignable to type Constructable<T>

Example in Playground, hover over Constructable in args to see error

Answer 1

我解决了这个问题，该问题是在未通过模型的情况下返回默认值（在本例中为通用对象）。通常，修复方法是：

从将模型键入为Constructable接口开始，改为使用Constructable<T> | object的并集类型。
更改将模型传递到对象的默认位置。
buildModel()函数检查模型的类型，如果它是对象，则返回传入的值，如果它是可构造的，则创建它的实例。

查看如何在postAsync参数中，在ResponseModel界面中以及在buildModel中实现的requestAsync方法中实现它：

interface Constructable<T> { new(params : any): T ;}
type ResponseModel<T> = Constructable<T> | Object;

export default class WebapiBase {
  static async postAsync<T = Object>(
      {
          uri = '',
          body = {},
          headers = new CustomHeaders(),
      }: PostRequestParams = {},
      // Here is where the defualt is implemented
      model: ResponseModel<T> = Object): Promise<T> {
      return this.requestAsync(model, HTTP_METHOD.POST, uri, headers, body);
  }
  private static async requestAsync<T = Object>(
      // This param accepts either a class or object
      model: ResponseModel<T>,
      method: HTTP_METHOD,
      uri: string,
      headers: CustomHeaders,
      body?: object): Promise<T> {
      const url = new URL(uri, window.location.origin);
      const request = this.buildRequest(url, method, headers, body);
      const bodyResponse = await fetch(request)
          .then(response => this.validate(response, request.headers))
          .then(validResponse => this.extractBody(validResponse))
          // Class instance or object returned here
          .then(extractedBody => this.buildModel(model, extractedBody))
          .catch((error) => { throw this.handleError(error); });
      return bodyResponse;
  }

  // Method that conditionally creates an instance of the passed in model
  // Or returns the object passed in if no model specified
  private static buildModel<T = Object>(
        Model: ResponseModel<T>,
        params: any,
    ): T {
        if (typeof Model === 'object') return params;
        return new Model(params);
  }
}

当参数的类型为泛型时，是否可以为打字稿中的参数设置默认值？

1 个答案: