Angular 6.x.x multipart form data post

form-data.js

// Completey omit the 'ContentType: multipart/form-data' headers
// const httpUploadOptions = {
//   headers: new HttpHeaders({
//     'Content-Type': 'multipart/form-data'
//   })
// };

const str = JSON.stringify('your Blob or Array');
const fd = new FormData();
const file = new File([str], 'fileName');
fd.append('file', file);

this.http.put('path/to/url', fd)
 .subscribe(
    data => this.data = data as any,
    err => 'do something with error'
  });