Easier use of indexed access types on nullable/optional types

🔍 Search Terms

index access types optional nullable

✅ Viability Checklist

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
• This isn't a request to add a new utility type: https://github.com/microsoft/TypeScript/wiki/No-New-Utility-Types
• This feature would agree with the rest of our Design Goals: https://github.com/Microsoft/TypeScript/wiki/TypeScript-Design-Goals

⭐ Suggestion

I would like a more succint way to access types from a nested object that contains nullable fields.

Possibly by allowing ! in a type-level position as a shorthand for NonNullable<T>

📃 Motivating Example

Generated types representing API responses often contain useful types that you'd prefer to extract rather than repeating them elsewhere. This comes up quite often for me when using graphql codegen on a query with a deeply nested response payload.

eg.

type APIResponse = {
	items: {
		id: string;
		author?: {
            id: string;
			name: string;
            status: "owner" | "admin" | "contributor" | "freeloader";
		}
	}[];
	pagination: {
		next_page: string;
	}
}

This example is a bit contrived, but is fairly representative of the general problem.

If I try and extract the status property, this doesn't work:

type APIAuthor = APIResponse['items'][0]['author']['status'];
//     Property 'status' does not exist on type '{ id: string; name: string; status: "owner" | "admin" | "contributor" | "freeloader"; } | undefined'.

Unless I wrap with NotNullable, and then it does.

type APIAuthor = NonNullable<APIResponse['items'][0]['author']>['status'];

Conceptually, I think the ! operator could work nicely here, giving us

type APIAuthor =APIResponse['items'][0]['author']!['status'];

💻 Use Cases

I've covered this a bit under the "motivating example" section, so maybe I've misused the headers a bit.

This comes up quite often for me when using graphql codegen on a query with a deeply nested response payload.

My current workaround is use of NonNullable, but when there's multiple layers of optionality it gets very difficult to follow.

Start with the motivating APIResponse example and compare the proposed type-level ! syntax with the existing NonNullable workaround. Determine the intended behavior for nested optional and nullable indexed accesses, then define acceptance cases showing that the shorthand produces the same extracted type without changing JavaScript output.