From https://stackoverflow.com/questions/46537790/iso8601-date-json-decoding-using-swift4

new_gist_file_0

enum DateError: String, Error {
    case invalidDate
}

struct Spaceship : Codable {
    var name: String
    var createdAt: Date
}

let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .custom({ (decoder) -> Date in
    let container = try decoder.singleValueContainer()
    let dateStr = try container.decode(String.self)

    let formatter = DateFormatter()
    formatter.calendar = Calendar(identifier: .iso8601)
    formatter.locale = Locale(identifier: "en_US_POSIX")
    formatter.timeZone = TimeZone(secondsFromGMT: 0)
    formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSXXXXX"
    if let date = formatter.date(from: dateStr) {
        return date
    }
    formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ssXXXXX"
    if let date = formatter.date(from: dateStr) {
        return date
    }
    throw DateError.invalidDate
})