We announced 5 years ago a plan to eventually make exact object types the default. We are now proceeding with this plan. Starting with Flow 0.200, you must explicitly set either exact_by_default=true or exact_by_default=false in the [options] section of your .flowconfig, as we have eliminated the default value (which was…

Flow handled the empty object literal {} in a permissive but unsafe way. The fix increases safety and predictability, but requires using different patterns and behavior described in this post. Flow treated the empty object literal {}as an object which could change over time as values were written to and…

The Flow team recently announced Flow Enums, a new language feature from Flow. If you’re familiar with TypeScript, you might be wondering how this feature compares to TypeScript’s enums. While they superficially look similar, they are quite different. This is an overview of some of the differences between TypeScript and…

As announced in an earlier post, Flow will be introducing new language features. The first one is Flow Enums, an opt-in feature which allows you to define a fixed set of constants which create their own type. …

Flow’s Indexed Access Types are a new type annotation syntax that allows you to get the type of a property from an object, array, or tuple type. They are a replacement for the $PropertyType and $ElementType type utilities. Not only are Indexed Access Types much more readable, but they also…