How to specify your own date format with Codable and JSONEncoder

Swift version: 5.1

Paul Hudson @twostraws May 28th 2019

When using JSONEncoder to encode dates, there are a handful of built-in date formats you can choose from. If none of them fit your needs, why not make your own? You can configure a DateFormatter using whatever date and time format you want, then pass that to the JSONEncoder as its dateEncodingStrategy property, like this:

let encoder = JSONEncoder()
let formatter = DateFormatter()
formatter.dateStyle = .full
formatter.timeStyle = .full
encoder.dateEncodingStrategy = .formatted(formatter)

That converts any Date properties to be the fullest possible string for your locale, e.g. "Monday, February 5, 2018 at 9:28:10 PM Greenwich Mean Time”.