Utility that fetches from a paginated resource by repeatedly fetching & concatenating pages

fetch_paginated.ts

// Fetch several rows from 1 or more pages from an API. Concatenate all
// the rows together.
function paginated<Request, Response, Row>(
  // A fetch function that retrieves a single page. Intended to wrap a fetch()
  // API call (so that you can add your own headers, auth, response parsing,
  // etc)
  fetcher: (url: Request, cancel?: AbortSignal) => Promise<Response>,

  // Given a response, get the URL of the next page, or null if this was the
  // last page.
  getNextRequest: (response: Response) => Request | null | undefined,

  // Given a response, get all the rows in the page. All the rows from all the
  // pages will be concatenated for the final response from fetch_paginated.
  // If each page is its own row, this can simply be `response => [response]`
  getRows: (response: Response, cancel?: AbortSignal) => Promise<Row[]>
): (request: Request, cancel?: AbortSignal) => Promise<Row[]> {
  const fetchPage = (
    request: Request,
    rows: Promise<Row[]>,
    cancel?: AbortSignal
  ): Promise<Row[]> =>
    fetcher(request, cancel).then((response) => {
      const nextRequest = getNextRequest(response);
      const nextRows = getRows(response, cancel);
      const allRows = Promise.all([rows, nextRows])
        .then(([rows, nextRows]) => rows.concat(nextRows))

      return nextRequest == null
        ? allRows
        : fetchPage(nextRequest, allRows, cancel);
    });

  return (request, cancel) => fetchPage(request, Promise.resolve([]), cancel);
}