FanDuel props in JavaScript and TypeScript

// Node 18+: fetch is built in. Keep the key on the server.
const BASE = "https://fanduelapi.com/api/v1";
const KEY = process.env.FANDUEL_API_KEY;

type Meta = { plan: string; delay_seconds: number; as_of: string; source_status: string };
type Body<T> = { data: T; meta: Meta & { has_more?: boolean; next_cursor?: string } };

export async function get<T>(path: string, params: Record<string, string | number> = {}): Promise<Body<T>> {
  const url = new URL(BASE + path);
  for (const [k, v] of Object.entries(params)) url.searchParams.set(k, String(v));
  for (;;) {
    const res = await fetch(url, { headers: { Authorization: `Bearer ${KEY}` } });
    if (res.status === 429) { await new Promise((r) => setTimeout(r, Number(res.headers.get("Retry-After") ?? 5) * 1000)); continue; }
    if (!res.ok) throw new Error(`${res.status} ${await res.text()}`);
    return res.json() as Promise<Body<T>>;
  }
}

type Prop = { id: string; player: string; stat: string; line: number | null; over_american: number | null; under_american: number | null; move: { line_moves: number } | null };

const { data, meta } = await get<Prop[]>("/props", { league: "NBA", stat: "points", limit: 50 });
console.log(`plan ${meta.plan}, ${meta.delay_seconds}s behind, as of ${meta.as_of}`);
for (const p of data) console.log(p.player.padEnd(24), p.line, p.over_american, p.under_american);

// Page through the whole board with limit and offset.
async function allProps(league: string) {
  const out: Prop[] = [];
  for (let offset = 0; ; offset += 200) {
    const page = await get<Prop[]>("/props", { league, limit: 200, offset });
    out.push(...page.data);
    if (!page.meta.has_more) return out;
  }
}

type History = {
  prop: { id: string; player: string; stat: string };
  move: { line_moves: number; price_moves: number } | null;
  history: { observed_at: string; line: number | null; over_american: number | null }[];
};
const { data: h } = await get<History>(`/props/${data[0].id}/history`);
console.log(`${h.prop.player}: opened ${h.history[0]?.line}, now ${h.history.at(-1)?.line}, ${h.history.length} states`);

// Stay current for one request per poll: read only what changed since your cursor.
let since = "0";
setInterval(async () => {
  const page = await get<{ kind: string; player: string; previous: unknown; current: unknown }[]>("/changes", { since, limit: 500 });
  for (const c of page.data) if (c.kind === "line_move") console.log(c.player, c.previous, "->", c.current);
  since = page.meta.next_cursor ?? since;
}, 15_000);

// Or let the server push: Server-Sent Events with resume.
const res = await fetch(`${BASE}/stream?league=NBA`, { headers: { Authorization: `Bearer ${KEY}`, Accept: "text/event-stream" } });
const reader = res.body!.pipeThrough(new TextDecoderStream()).getReader();
let buffer = "";
for (;;) {
  const { value, done } = await reader.read();
  if (done) break;
  buffer += value;
  let end;
  while ((end = buffer.indexOf("\n\n")) >= 0) {
    const frame = buffer.slice(0, end); buffer = buffer.slice(end + 2);
    const data = frame.split("\n").find((l) => l.startsWith("data: "));
    if (data) console.log(JSON.parse(data.slice(6)));
  }
}