附加[object％20Object]的angular 2 http删除参数url

Question

我在角度2中使用http.delete。这是我的代码

app.component.ts

deleteCourse(id: string)  {
       console.log(id);
       this.appService.deleteByID(id)

       .subscribe(x => {console.log(x); this.fetchCourseData(); }

        );
   }

app.service.ts

deleteByID(id: string): Observable<string> 

    let options1 = new RequestOptions();
    options1.headers = new Headers();
    options1.headers.append('Content-Type', 'application/json');
   return this.http.delete('http://localhost:3000/sample'+ '/' + id , options1)
     .map((response: Response) => {
            const result = response.json();
            return result; });
}

db.json

{
  "sample": [
    {

    {
      "courseTitle": "ggg",
      "courseDescription": "ggg",
      "courseCredit": "2",
      "id": 8
    },
    {
      "courseTitle": "ggg",
      "courseDescription": "ggg",
      "courseCredit": "1",
      "id": 9
    },
    {
      "courseTitle": "add",
      "courseDescription": "asdas",
      "courseCredit": "2",
      "id": 10
    }
  ]
}

网址传递为 http://localhost:3000/sample/[object%20Object]

以及404错误。我如何纠正这个问题？