Typescript type returned by getFields()

[IanVS]

I'm wondering if the typescript types for getFields() is correct, because it is defined as returning this:

export type GraphQLFieldMap<
  TSource,
  TContext,
  TArgs = { [key: string]: any }
> = {
  [key: string]: GraphQLField<TSource, TContext, TArgs>;
};

Which means that type.getFields().foobar will always be treated as truthy, even if no such field exists in the schema, right? I feel like maybe I'm missing something, but I would have expected to get back something more like:

export type GraphQLFieldMap<
  TSource,
  TContext,
  TArgs = { [key: string]: any }
> = {
  [key: string]: GraphQLField<TSource, TContext, TArgs> | undefined;
};

Is this an issue, or something I'm misunderstanding?

[agammann]

Your reading is right. getFields() returns a string-keyed map, so with TypeScript's default index-signature behavior, getFields().foobar has the value type even when that key is absent at runtime. It doesn't mean the field exists.

If you enable noUncheckedIndexedAccess in tsconfig.json, an indexed lookup becomes GraphQLField | undefined and TypeScript requires a guard:

const field = type.getFields()[fieldName]
if (!field) {
  throw new Error(`Unknown field: ${fieldName}`)
}
// field is now a GraphQLField

I checked this with GraphQL.js 17.0.2 and TypeScript 5.9.3: a missing field is undefined at runtime, and the compiler catches an unguarded lookup with that option enabled. This is the general TypeScript noUncheckedIndexedAccess behavior.