Private Object Properties Using Flow’s Opaque Type Aliases

:::info[Historical] This post announced private object properties using opaque types when it was introduced. For current syntax and behavior, see the Opaque Types documentation. :::

In the last few weeks, a proposal for private class fields in Javascript reached stage 3. This is going to be a great way to hide implementation details away from users of your classes. However, locking yourself in to an OOP style of programming is not always ideal if you prefer a more functional style. Let’s talk about how you can use Flow’s opaque type aliases to get private properties on any object type.