Let’s say we have an string enum in TypeScript, and we want to use those enum values as keys in another object.

There’s potential that we might forget to add a matching entry to our object when updating or renaming a member of the enum, which may not be desirable. This post describes a quick trick to ensure this at compile time.

Typescript Type

Instead of Record<Key1|Key2, ValueType>, we can use the EnumRecord<MyEnum, ValueType> on our record, and it will require that all of the values of the enum are exhaustively defined as members in our object:

type EnumRecord<KeyType extends string, ValueType> = {[key in KeyType]: ValueType};

In practice

For a practical example, we could have some code like this:

// require all enum keys on record
type EnumRecord<KeyType extends string, ValueType> = {[key in KeyType]: ValueType};

// some keys to use
enum FeatureFlagKeys {
  DarkMode = 'dark_mode'
  DashboardMetrics = 'dashboard_metrics'
  CommentsView = 'comments_view'
}

// an object using enum values as keys
const FlagMetadata : EnumRecord<FeatureFlagKeys, { title: string }> = {
  [FeatureFlagKeys.DarkMode]: { title: 'Dark Mode' },
  [FeatureFlagKeys.DashboardMetrics]: { title: 'Enhanced Dashboard Metrics' },
}

Resulting Error

When we compile the above example, this will yield an error on typescript compilation, since FeatureFlagKeys.CommentsView is missing:

Property '[FeatureFlagKeys.CommentsView]' is missing in type '{ dark_mode: { title: string; }; dashboard_metrics: { title: string; }; }' but required in type 'EnumRecord<FeatureFlagKeys, { title: string; }>'. ts(2741)