angular - Angular 8 中的错误 : Type 'string' is not assignable to type '"body"'.

Question

ERROR in src/app/new-applicant/new-applicant.service.ts(35,65): error TS2345: Argument of type '{ reportProgress: boolean; observe: string; headers: HttpHeaders; }' is not assignable to parameter of type '{ headers?: HttpHeaders | { [header: string]: string | string[]; }; observe?: "body"; params?: HttpParams | { [param: string]: string | string[]; }; reportProgress?: boolean; responseType?: "json"; withCredentials?: boolean; }'. Types of property 'observe' are incompatible. Type 'string' is not assignable to type '"body"'.

    public generateHeaders()
    {
        let access=JSON.parse(sessionStorage.getItem("meta_info")).access
        // access=access.access;
        console.log(access)
        var headers_object = new HttpHeaders().set("Authorization", "Bearer " + access);
        const httpOptions = {
            reportProgress:true,
            observe:'events',
            headers: headers_object
        };
        return httpOptions
    }

服务

  public registerNewApplicant(data)
  {
    return this.http.post(environment.baseURL+"applicant/",data,this.jwtTokenGenerator.generateHeaders())
  }

Answer 1

使用 as const强制 TypeScript 推断 observe 的类型作为文字类型 "events"而不是 string :

observe: 'events' as const,

HttpClient 中的每个方法都有一堆重载，期望 observe是以下之一: "body" , "events" , "response" .

默认情况下，TypeScript 将字符串文字的类型推断为 string ，除非在某些情况下，例如初始化 const或 readonly领域。 generateHeaders的返回类型最终成为

{ reportProgress: boolean; observe: string; headers: HttpHeaders; }

关于 observe的信息正在 "events"丢失，因此该值与任何重载都不匹配。