Load dynamically file in the angular using service

script-loader.service.ts

import { Injectable } from '@angular/core';

@Injectable()
export class ScriptLoaderService {
  constructor() { }

  loadScript(url: string) {
    return this.load(url, 'script');
  }

  loadStyle(url: string) {
    return this.load(url, 'stylesheet');
  }

  private load(url: string, type: 'script' | 'stylesheet') {
    return new Promise((resolve, error) => {
      let node;
      let isScript: HTMLElement;

      switch (type) {
        case 'script':
          isScript = Array.from(document.getElementsByTagName('script'))
            .find(res => res.getAttribute('src') != null && res.getAttribute('src').includes(url));
          if (!isScript) {
            node = document.createElement('script');
            node.type = 'text/javascript';
            node.src = url;
          }
          break;
        case 'stylesheet':
          isScript = Array.from(document.getElementsByTagName('link'))
            .find(res => res.getAttribute('href') != null && res.getAttribute('href').includes(url));

          if (!isScript) {
            node = document.createElement('link');
            node.rel = 'stylesheet';
            node.href = url;
          }
      }

      if (isScript && isScript.classList.contains('file-loaded-script-loader')) {
        return resolve();
      } else if (isScript) {
        return isScript.onload = () => {
          resolve();
        }
      }

      node.async = false;
      node.charset = 'utf-8';
      document.getElementsByTagName('head')[0].appendChild(node);
      node.onload = () => {
        node.classList.add('file-loaded-script-loader');
        resolve();
      };
      node.onerror = () => {
        error();
      }
    });
  }

}