Iterator / generator

type Application = { name: string };
type Page = { applications: Application[]; next: string | null };

// The job board's API for one post: applications, newest first, a page at a time.
// Checker plumbing: the checker builds a board for each case. You don't need to edit it.
class JobBoard {
  log: string[] = [];
  private pages: Application[][];
  constructor(pages: string[][]) {
    this.pages = pages.map((page) => page.map((name) => ({ name })));
  }
  open(): void {
    this.log.push('open');
  }
  // '' asks for the first page; each page's next token asks for the one after it.
  fetch(token: string): Page {
    const number = token === '' ? 1 : Number(token.slice(1));
    this.log.push(`page ${number}`);
    const next = number < this.pages.length ? `c${number + 1}` : null;
    return { applications: this.pages[number - 1], next };
  }
  close(): void {
    this.log.push('close');
  }
}

// The one traversal both callers should share. Not written yet: it yields nothing.
function* applications(board: JobBoard): Generator<Application> {}

// The review screen's first view: the newest `count` applications.
function newest(board: JobBoard, count: number): string[] {
  board.open();
  const all: string[] = [];
  let token: string | null = '';
  while (token !== null) {
    const page = board.fetch(token);
    for (const application of page.applications) all.push(application.name);
    token = page.next;
  }
  board.close();
  return all.slice(0, count);
}

// The search box: has this person applied?
function hasApplied(board: JobBoard, name: string): boolean {
  board.open();
  let token: string | null = '';
  while (token !== null) {
    const page = board.fetch(token);
    if (page.applications.length === 0) break; // nothing left
    for (const application of page.applications) {
      if (application.name === name) return true;
    }
    token = page.next;
  }
  board.close();
  return false;
}