The system is failing to recognize the union data type

Question

The system is failing to recognize the union data type

My code defines various types as follows:

export type Property =
  | BooleanProperty
  | NumberProperty
  | IntegerProperty
  | StringProperty
  | ObjectProperty
  | ArrayProperty;

export interface OneOf {
  oneOf: PropertyOrKeyword[];
}
export interface AnyOf {
  anyOf: PropertyOrKeyword[];
}
type Keyword = OneOf | AnyOf;
export type PropertyOrKeyword = Property | Keyword;

Later in the code, I have the following snippet:

const val = parent[objName]; // This variable is of type 'PropertyOrKeyword'
if ("oneOf" in parent[objName]) {
  const index = val.oneOf.findIndex(
    (obj: Property) => obj.title === title
  );
  val.oneOf[index] = ref(title);
}

However, when hovering over val.oneOf, an error is displayed:

Error: Property 'oneOf' does not exist on type 'PropertyOrKeyword'.
  Property 'oneOf' does not exist on type 'BooleanProperty'.

It seems like there might be an issue with the unioned types causing TypeScript to overlook the existence of the 'oneOf' field. Could it be related to the recursive nature of these types? The use of the in operator should theoretically help TypeScript infer that val is of type OneOf.

Am I overlooking something important here?

typescript

Answer 1

Answer №1

Even though the assignment is done at the line before the check, TypeScript fails to recognize that val and parent[objName] refer to the same object. It is advisable to directly access the val property for accurate results.

const val = parent[objName]; // This is a PropertyOrKeyword type
if (typeof val === "object" && "oneOf" in val) {
  const index = val.oneOf.findIndex(
    (obj: Property) => (obj as ({title: string})).title === title
  );
  val.oneOf[index] = ref(title);
}

For further understanding and modification of your code, you can visit this TS Playground link.

Furthermore, it is recommended to verify if the obj contains a title property or cast it as { title: string } while comparing values in the findByIndex callback function.

Answer 2

Even though the assignment is done at the line before the check, TypeScript fails to recognize that val and parent[objName] refer to the same object. It is advisable to directly access the val property for accurate results.

const val = parent[objName]; // This is a PropertyOrKeyword type
if (typeof val === "object" && "oneOf" in val) {
  const index = val.oneOf.findIndex(
    (obj: Property) => (obj as ({title: string})).title === title
  );
  val.oneOf[index] = ref(title);
}

For further understanding and modification of your code, you can visit this TS Playground link.

Furthermore, it is recommended to verify if the obj contains a title property or cast it as { title: string } while comparing values in the findByIndex callback function.

The system is failing to recognize the union data type

Answer №1

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