Sometimes, we want to use enum as index key type in TypeScript.

In this article, we’ll look at how to use enum as index key type in TypeScript.

How to use enum as index key type in TypeScript?

To use enum as index key type in TypeScript, we can use the in operator.

For instance, we write

enum DialogType {
  Options,
  Help,
}

const openDialogs: { [key in DialogType]?: Dialog } = {
  [DialogType.Options]: undefined,
};

to create the DialogType enum.

Then we use it in a type by setting openDialogs to the { [key in DialogType]?: Dialog } type.

We set the index signature’s type to key in DialogType to make sure the keys of openDialogs must be any one of the DialogType enum values.

Therefore, using [DialogType.Options] as a key value wouldn’t make the TypeScript compiler raise an error.

Conclusion

To use enum as index key type in TypeScript, we can use the in operator.