GraphQLTypedMapType

How do you specify this Typescript in GraphQL?:

interface MyType {
  [propName: string]: MyOtherType
}

AFAIK you can't. You have to define all the fields of an object explicitly if you want to specify the types of those fields.

graphql-type-json provides GraphQLJSONObject which allows for an arbitrary object. This simple package provides GraphQLTypedMapType() which produces a GraphQLScalarType type that allows you to declare a more constrained type of object like the Typescript above. It also allows your to optionally constrain which keys can be present at the top level.

Note, the downside of defining custom scalar types is since the type is not part of GraphQL SDL, the client side can't know in advance whether a type valid for custom scalar types.

Protocol:

GraphQLTypedMapType = (name: string, allowedKeys?: string[], valueType?: any): GraphQLScalarType

Usage:

// name parameter is required and must be unique.
const type1: GraphQLScalarType = GraphQLTypedMapType("MyMap1", undefined, GraphQLString); // no key constraints.
const type2: GraphQLScalarType = GraphQLTypedMapType("MyMap2", ['a','b','c'], GraphQLInt); // some key constraints.