Use generic type for FormulaPropertyItemObjectResponse

[believelody]

This issue is a suggestion.

Describe the bug
When dealing with formula property, I noticed :

type FormulaPropertyResponse = StringFormulaPropertyResponse | DateFormulaPropertyResponse | NumberFormulaPropertyResponse | BooleanFormulaPropertyResponse;

This way, if I have 2 properties in my datasource (one string, other a date), typescript cannot give me the corresponding type.

To Reproduce
Node version: 24.11.1
Notion JS library version: 5.6.0

Steps to reproduce the behavior:

• Have at least one formula property in database ;
• Make a datasource query with notion sdk ;
• Retrieve formula value

Expected behavior
Currently I use this workaround :

{
          id: result.id,
          slug:
            "string" in properties.slug.formula &&
            properties.slug.formula.string
              ? properties.slug.formula.string
              : ""
}

I have to manually check if formula contains the wanted value.

We can solve this by doing this way :

export type FormulaPropertyItemObjectResponse<T extends string | Date | number | boolean> = {
    type: "formula";
    formula: FormulaPropertyResponse<T>;
    object: "property_item";
    id: string;
};
type FormulaPropertyResponse<T extends string | Date | number | boolean> = T extends string ? StringFormulaPropertyResponse : T extends Date ? DateFormulaPropertyResponse : T extends number ? NumberFormulaPropertyResponse : T extends boolean  ? BooleanFormulaPropertyResponse : never;

Usage :

export type NotionArticleDTO = {
  slug: FormulaPropertyItemObjectResponse<string>;
  title: TitlePropertyItemObjectResponse;
  publishedAt: FormulaPropertyItemObjectResponse<Date>;
  status: StatusPropertyItemObjectResponse;
  category: SelectPropertyItemObjectResponse;
};

What do you think about that ?

[larveen667-a11y]

export type FormulaPropertyItemObjectResponse<T extends string | Date | number | boolean> = {
type: "formula";
formula: FormulaPropertyResponse;
object: "property_item";
id: string;
};
type FormulaPropertyResponse<T extends string | Date | number | boolean> = T extends string ? StringFormulaPropertyResponse : T extends Date ? DateFormulaPropertyResponse : T extends number ? NumberFormulaPropertyResponse : T extends boolean ? BooleanFormulaPropertyResponse : never;

[larveen667-a11y]

#654

[believelody]

export type FormulaPropertyItemObjectResponse<T extends string | Date | number | boolean> = {
type: "formula";
formula: FormulaPropertyResponse;
object: "property_item";
id: string;
};
type FormulaPropertyResponse<T extends string | Date | number | boolean> = T extends string ? StringFormulaPropertyResponse : T extends Date ? DateFormulaPropertyResponse : T extends number ? NumberFormulaPropertyResponse : T extends boolean ? BooleanFormulaPropertyResponse : never;

I didn't understand. This is what I suggested !