[BrandonM]

From the article:

    this.downloadService.fileWithProgress(url, 'POST', 'download', body);

    ...

    public fileWithProgress(url: string, reqType: RequestType, actionType: ActionType, body: ...): void {
        ...
    }
    ...
    export type RequestType = 'GET' | 'POST' | ...;
    export type ActionType = 'download' | ...;