Post image/file (multipart) with Angular6 - json

Question

I try to post an image with http.post from Angular6.
See below my rest service and component.
Service
setOptions(data: boolean = false, headersToSet?: any): any {
let token: string;
const headers = [];
token = JSON.parse(localStorage.getItem('SOSF_MANAGER_TOKEN'));
// AUTHORIZATION
headers['Authorization'] = 'Bearer ' + token;
headers['Content-Type'] = data ? 'multipart/form-data' : 'application/json';
// OTHER HEADERS
if (headersToSet !== undefined) {
for (const headerName of Object.keys(headersToSet)) {
headers[headerName] = headersToSet[headerName];
}
}
return { headers };
}
// POST
postDb(url: string, body: any): Observable<any> {
let options: any;
options = this.setOptions(body instanceof FormData);
url = this.url + url;
if (!(body instanceof FormData)) {
body = JSON.stringify(body);
} else {
// TO DO
}
console.log(body);
if (environment.console_log_construct) {
console.log(`POST : ${url}`);
}
return this.http.post(url, body, options).pipe(
map(response => {
return response;
}, error => {
console.error(`POST ERROR: ${url}`, error);
}));
}
Component
// Open Our formData Object
const formData = new FormData();
// Append our file to the formData object
formData.append('file', files[0]);
// POST
this.restService.postDb('files/images', formData)
.subscribe(response => {});
If I let JSON.stringify(body) when body is formData, formdata is set to {}. But if I let body like this, it throw a error 'Uncaught SyntaxError: Unexpected token o in JSON at position 1'. How can I achieve it ?