[SOLVED] How to get "to_do" from a notion block using typescript?

Issue

Recently I tried final version of Notion API. Using typescript I made a retrieve block children request:

(async () => {
    const blockId = process.env.BLOCK_ID;
    const response = await notion.blocks.children.list({
        block_id: blockId,
        page_size: 50,
    });
    console.log(response.results[1].to_do);
})();

Error message

For some reason typescript tells me that to_do doesn’t exist in type (PartialBlockObjectResponse | BlockObjectResponse). I looked at type definition and… it was there:

declare type BlockObjectResponse = {
    // ...
    {
    type: "to_do";
    to_do: {
        rich_text: Array<RichTextItemResponse>;
        color: ApiColor;
        checked: boolean;
    };
    object: "block";
    id: string;
    created_time: string;
    created_by: {
        id: IdRequest;
        object: "user";
    };
    last_edited_time: string;
    last_edited_by: {
        id: IdRequest;
        object: "user";
    };
    has_children: boolean;
    archived: boolean;
} 
// ...
}

I tried making type guard

function isToDo(value: PartialBlockObjectResponse | BlockObjectResponse): value is BlockObjectResponse {
     return "to_do" in value;
}  /* Error: TS2304: Cannot find name 'PartialBlockObjectResponse'. */

and importing type from package

import type {PartialBlockObjectResponse} from "@notionhq/client/build/src/api-endpoints"; 
// Error: Module '"@notionhq/client/build/src/api-endpoints"' declares 'PartialBlockObjectResponse' locally, but it is not exported.

Neither helped.

Solution

(Frustratingly) That package does not export its types. There’s an open issue about it in the repo.

But you can work around this using a generic with your predicate function:

TS Playground

import {Client} from '@notionhq/client';
declare const notion: Client;
declare const blockId: string;

function isTodo <T extends Record<string, unknown>>(obj: T): obj is T & { type: 'to_do' } {
  return 'type' in obj && obj.type === 'to_do';
}

(async () => {
  const response = await notion.blocks.children.list({block_id: blockId, page_size: 50});

  for (const result of response.results) {
    if (isTodo(result)) {
      result.to_do; /*
             ^^^^^
      is now this type:
      {
          rich_text: RichTextItemResponse[];
          color: ApiColor;
          checked: boolean;
      }
      */
    }
  }
})()

Answered By – jsejcksn

Answer Checked By – Dawn Plyler (BugsFixing Volunteer)