jsonp to get douabn isbn data

douban.service.ts

import { Injectable } from '@angular/core';
import {Md5} from "md5-typescript";

const remove_timeout = 20000;

@Injectable({
  providedIn: 'root'
})
export class DoubanService {
  private apiRoot = 'https://api.douban.com/v2/book';

  constructor() {}

  searchISBN(isbn: string) {
    return new Promise((resolve, reject) => {
      let timeId;
      const hash_str = Md5.init(isbn);
      const callbackName =  `jsonp_${hash_str}`;
      const url = `${this.apiRoot}/isbn/${isbn}?callback=${callbackName}`;
      const scriptElem = window.document.createElement('script');
      // clear all
      const clearFunction = () => {
        window.document.body.removeChild(scriptElem);
        delete window[callbackName];
      };
      // sucess
      window[callbackName] = res => {
        resolve(res);
        timeId = setTimeout(clearFunction, remove_timeout);
      };
      // fail
      scriptElem.onerror = () => {
        reject(new Error(`failed to get ${url}!`));
        clearFunction();
        if (timeId) { clearTimeout(timeId); }
      };
      scriptElem.id = callbackName;
      scriptElem.src = url;
      scriptElem.type = 'text/javascript';
      window.document.body.appendChild(scriptElem);
    });
  }
}