Javascript:什么是Http服务中的reportProgress？

import { HttpClient } from '@angular/common/http';

constructor(private http: HttpClient) {}

uploadFile(file: File) {
  const url = 'https://api.example.com/upload';
  const formData = new FormData();
  formData.append('file', file);

  this.http.post(url, formData, {
    reportProgress: true, // 启用进度报告
    observe: 'events' // 返回完整的事件对象
  }).subscribe(event => {
    if (event.type === HttpEventType.UploadProgress) {
      const progress = Math.round(100 * event.loaded / event.total);
      console.log(`Uploading: ${progress}%`);
    } else if (event.type === HttpEventType.Response) {
      console.log('Upload complete');
    }
  });
}