How can I know possible values for __typename for schema objects that implement node interface?

[xoldd]

@n1ru4l

There's no explicit way to know what the possible values for __typename field are i.e., what schema objects implement node interface. Typescript intellisense for possible values of __typename for a node interface object only kicks in when we're returning a response object inside the node query resolver.

Let's say I have utility functions like encodeGlobalId and decodeGlobalId, how would I restrict the possible values for __typename that are passed in our given out from these functions? Currently I'd have to manually check my graphql schema definition and create something like a union type for those values manually.

Currently I do something like this:-

export type NodeInterfaceTypeName = "User" | "Post" | "Group";

With this we can restrict typenames passed or given out by those utility functions:-

// By providing the union type NodeInterfaceTypeName, we can restrict what can be passed in as first parameter inside
// encodeGlobalId function. This will prevent us from passing in wrong values for __typename.
const userGlobalId = encodeGlobalId<NodeInterfaceTypeName>("__typename", userId);

// By providing the union type NodeInterfaceTypeName, we can expect what can be given out as __typename inside the object
// returned by decodeGlobalId function.
const { __typename, id } = decodeGlobalId<NodeInterfaceTypeName>(userGlobalId);
// __typename will be type safe here and will be of NodeInterfaceTypeName union type instead of a typescript string type.
if ( __typename !== "User") {  
  ...do something
}

// Or even better, NodeInterfaceTypeName can be hard coded into the utility functions themselves.

If this is something that's already possible(some typescript trick maybe?) let me know. If not this can be issued as a feature request with proper details.