Reddit API in JavaScript

// No package to install for a plain script. fetch is global in Node 18+
// and in every browser, so there is zero dependency for the calls below.
export REDDITAPIS_KEY="rk_live_your_key_here"

const BASE_URL = "https://api.redditapis.com";

async function redditApi(path, params = {}) {
  const url = new URL(BASE_URL + path);
  for (const [k, v] of Object.entries(params)) url.searchParams.set(k, v);
  const res = await fetch(url, {
    headers: { Authorization: `Bearer ${process.env.REDDITAPIS_KEY}` },
  });
  if (!res.ok) {
    const body = await res.json().catch(() => ({}));
    throw Object.assign(new Error(body.error || res.statusText), { status: res.status });
  }
  return res.json();
}

const { posts } = await redditApi("/api/reddit/posts", {
  subreddit: "webdev",
  sort: "top",
  t: "week",
  limit: 25,
});
for (const post of posts) console.log(post.upvotes, post.title, post.permalink);

// Site-wide post search. Drop subreddit and it searches all of Reddit.
// min_score and is_self apply to the returned page; the response reports how
// many rows the filters removed in meta, when any filter is set.
const { posts: searchResults } = await redditApi("/api/reddit/search", {
  q: "postgres connection pooling",
  subreddit: "devops",
  sort: "relevance",
  t: "month",
  limit: 50,
  min_score: 20,
  is_self: "true",
});

for (const p of searchResults) console.log(p.subreddit, p.author, p.title, p.url);

// Walk a subreddit listing with the cursor the API hands back. Pass `after`
// straight back on the next request; stop when it comes back null.
//
// A null cursor means there is no next page to ask for. It does NOT mean you
// have every post: Reddit often stops serving a busy listing early. The final
// response carries `listing_status`, and only "complete" means nothing is
// missing. "truncated" and "unknown" both mean your result has a gap.
async function* iterPosts(subreddit, maxPages = 5) {
  let cursor;
  for (let i = 0; i < maxPages; i++) {
    const params = { subreddit, sort: "new", limit: 100 };
    if (cursor) params.after = cursor;
    const body = await redditApi("/api/reddit/posts", params);
    yield* body.posts;
    cursor = body.after;
    if (!cursor) {
      if (body.listing_status !== "complete") {
        console.warn(`incomplete (${body.listing_status}): widen across sorts or timeframes`);
      }
      return;
    }
  }
}

let count = 0;
for await (const _post of iterPosts("rust")) count++;
console.log(count, "posts across at most 5 pages, 5 reads, $0.010");

// The new-comment stream for one subreddit, the read a keyword monitor polls.
const { comments } = await redditApi("/api/reddit/sub/devops/comments", { limit: 100 });

for (const c of comments) {
  if (c.body.toLowerCase().includes("kubernetes")) {
    console.log(c.author, c.subreddit, c.upvotes, c.url);
  }
}

// Deep comment search reads the comment TREES behind matching threads, so it
// returns real comment bodies rather than parent posts. One call fans out into
// a search plus several tree reads, priced at $0.02 instead of $0.002.
const body = await redditApi("/api/reddit/search/comments/deep", {
  q: "vector database",
  limit: 10,
  max_comments: 50,
});

for (const c of body.comments) {
  console.log(c.score, c.author, c.permalink);
  console.log("  thread:", c.parent_post.title);
}

console.log(body.meta.comments_matched, "matched,", body.meta.comments_returned, "returned");

// 402 and 403 are terminal: no retry buys credits or fixes a bad key.
// 429 and 503 are transient and safe to retry.
const TERMINAL = new Set([400, 401, 402, 403, 404]);
const RETRYABLE = new Set([429, 500, 502, 503, 504]);

async function callWithRetry(path, params, attempts = 4) {
  let delay = 1000;
  for (let i = 0; i < attempts; i++) {
    const url = new URL(BASE_URL + path);
    for (const [k, v] of Object.entries(params)) url.searchParams.set(k, v);
    const res = await fetch(url, {
      headers: { Authorization: `Bearer ${process.env.REDDITAPIS_KEY}` },
    });
    if (res.ok) return res.json();
    const body = await res.json().catch(() => ({}));
    if (TERMINAL.has(res.status) || !RETRYABLE.has(res.status)) {
      throw Object.assign(new Error(body.error || res.statusText), { status: res.status });
    }
    // The 429 carries Retry-After in seconds. Honour it before backing off.
    const retryAfter = Number(res.headers.get("Retry-After")) || delay / 1000;
    await new Promise((r) => setTimeout(r, retryAfter * 1000));
    delay *= 2;
  }
  throw new Error(`gave up after ${attempts} attempts`);
}

// GET /account/me is free and never consumes credits. Poll it from a
// scheduled job so a long run never dies halfway through on an empty balance.
const account = await redditApi("/account/me");
console.log(account.credits_remaining, "left");
console.log(account.credits_used, "spent over", account.total_requests, "requests");

// Every billed response also carries the balance in a header, so a worker
// can watch it without a second request.
const res = await fetch(new URL(BASE_URL + "/api/reddit/posts?subreddit=node&limit=5"), {
  headers: { Authorization: `Bearer ${process.env.REDDITAPIS_KEY}` },
});
console.log(res.headers.get("X-Credits-Remaining"));