WrapingFunctionWithPromise.swift

func promiseFetchJSON() -> Promise<[String: Any]> {
        return Promise<[String: Any]> { seal in
            fetchJSON(fromURL: "someURL", completion: { (response, results, error) in
                switch response {
                case .success:
                    seal.fulfill(results)
                case .fail:
                    seal.reject(error)
                }
            })
        }
    }