Live Odds API in Node.js: Build a WebSocket Odds Tracker

10:30:44 FK Iskra v Mladost Donja Gorica home none -> 4.76 Polymarket draw none -> 5.56 Polymarket away none -> 1.32 Polymarket 10:30:44 RB Leipzig v Mlada Boleslav home none -> 1.53 Bet365 draw none -> 5.30 Unibet away none -> 8.00 Unibet 10:30:44 snapshot: 2 live events, 2 with ML prices, seq 2874836490 10:30:44 connected, 8 bookmakers on this key 10:30:44 caught up (replayed), seq 2874836509 10:31:15 RB Leipzig v Mlada Boleslav draw 5.30 Unibet -> 5.25 Unibet away 8.00 Unibet -> 7.50 Unibet 10:31:17 RB Leipzig v Mlada Boleslav home 1.53 Bet365 -> 1.55 DraftKings 10:31:35 FK Iskra v Mladost Donja Gorica no ML prices left 10:31:40 FK Iskra v Mladost Donja Gorica home none -> 5.00 Polymarket draw none -> 5.26 Polymarket away none -> 1.51 Polymarket 10:31:54 disconnected, reconnecting in 1124 ms from seq 2874865192 10:31:55 connected, 8 bookmakers on this key 10:31:55 caught up (replayed), seq 2874866858 10:32:11 RB Leipzig v Mlada Boleslav home 1.55 DraftKings -> 1.57 Bet365 10:32:13 RB Leipzig v Mlada Boleslav away 7.50 Unibet -> 8.00 Unibet 

npm install odds-api-io ws 

// Live odds tracker: best match-winner price per outcome for one league, over WebSocket. // npm install odds-api-io ws // ODDS_API_KEY=... node tracker.mjs [league-slug] import { OddsAPIClient, OddsWebSocket } from 'odds-api-io'; const apiKey = process.env.ODDS_API_KEY; if (!apiKey) { console.error('Set ODDS_API_KEY first.'); process.exit(1); } const SPORT = 'football'; const LEAGUE = process.argv[2] ?? 'england-premier-league'; const MARKET = 'ML'; const OUTCOMES = ['home', 'draw', 'away']; const client = new OddsAPIClient({ apiKey }); let prices = new Map(); // eventId -> Map(bookmaker -> { home, draw, away }) const best = new Map(); // eventId -> { home: { price, bookie }, ... } const names = new Map(); // eventId -> "Home v Away" let touched = new Set(); // "eventId:bookmaker" pairs seen since the last welcome let feed; let resyncing = false; const log = (text) => console.log(`${new Date().toISOString().slice(11, 19)} ${text}`); const sleep = (ms) => new Promise((resolve) => setTimeout(resolve, ms)); function chunk(list, size) { const out = []; for (let i = 0; i < list.length; i += size) out.push(list.slice(i, i + size)); return out; } function readPrices(markets) { const line = markets.find((m) => m.name === MARKET)?.odds?.[0]; if (!line) return null; const out = {}; for (const outcome of OUTCOMES) { const price = Number.parseFloat(line[outcome]); if (price > 1) out[outcome] = price; } return Object.keys(out).length ? out : null; } function eventName(id) { if (!names.has(id)) { names.set(id, `event ${id}`); client .getEventById(id) .then((e) => names.set(id, `${e.home} v ${e.away}`)) .catch(() => {}); } return names.get(id); } function fmt(entry) { return entry ? `${entry.price.toFixed(2)} ${entry.bookie}` : 'none'; } function refreshBest(id) { const books = prices.get(id); const prev = best.get(id) ?? {}; const next = {}; for (const outcome of OUTCOMES) { for (const [bookie, p] of books ?? []) { const price = p[outcome]; if (!price) continue; const current = next[outcome]; if (!current || price > current.price || (price === current.price && bookie === prev[outcome]?.bookie)) { next[outcome] = { price, bookie }; } } } const changes = OUTCOMES.filter( (o) => prev[o]?.price !== next[o]?.price || prev[o]?.bookie !== next[o]?.bookie ).map((o) => `${o} ${fmt(prev[o])} -> ${fmt(next[o])}`); if (books?.size) { if (changes.length) log(`${eventName(id)} ${changes.join(' ')}`); best.set(id, next); } else { if (best.has(id)) log(`${eventName(id)} no ${MARKET} prices left`); prices.delete(id); best.delete(id); } } // Every odds message carries the full market set for the pair: replace, never merge. function apply(eventId, bookie, markets) { const id = String(eventId); touched.add(`${id}:${bookie}`); const latest = readPrices(markets); let books = prices.get(id); if (latest) { if (!books) prices.set(id, (books = new Map())); books.set(bookie, latest); } else { books?.delete(bookie); } refreshBest(id); } // After a state snapshot, pairs the server did not resend are gone. function dropUntouched() { for (const [id, books] of prices) { for (const bookie of books.keys()) { if (!touched.has(`${id}:${bookie}`)) books.delete(bookie); } refreshBest(id); } } // REST snapshot of every live event in the league, plus the stream position it matches. async function loadSnapshot() { const events = await client.getEvents({ sport: SPORT, league: LEAGUE, status: 'live' }); for (const e of events) names.set(String(e.id), `${e.home} v ${e.away}`); const fresh = new Map(); let seq = null; if (events.length) { const { bookmakers } = await client.getSelectedBookmakers(); for (const eventIds of chunk(events.map((e) => e.id), 10)) { for (const books of chunk(bookmakers, 30)) { const page = await client.getOddsSnapshot({ eventIds, bookmakers: books, markets: [MARKET] }); if (page.seq === null) throw new Error('snapshot came back without a seq'); seq = seq === null ? page.seq : Math.min(seq, page.seq); for (const event of page.data) { for (const [bookie, markets] of Object.entries(event.bookmakers)) { const latest = readPrices(markets); if (!latest) continue; const id = String(event.id); if (!fresh.has(id)) fresh.set(id, new Map()); fresh.get(id).set(bookie, latest); } } } } } return { fresh, seq, count: events.length }; } async function rebuild() { for (let attempt = 1; ; attempt++) { try { const { fresh, seq, count } = await loadSnapshot(); const ids = new Set([...prices.keys(), ...fresh.keys()]); prices = fresh; for (const id of ids) refreshBest(id); log(`snapshot: ${count} live events, ${fresh.size} with ${MARKET} prices, seq ${seq ?? 'none'}`); return seq; } catch (err) { if ([400, 401, 403, 404].includes(err.status)) throw err; const delay = Math.min(30_000, 1000 * 2 ** attempt); log(`snapshot failed (${err.name}), retrying in ${delay} ms`); await sleep(delay); } } } async function resync(reason) { if (resyncing) return; resyncing = true; log(`resync required (${reason}), rebuilding from REST`); const old = feed; feed = null; old.close(); try { await connect(await rebuild()); } catch (err) { log(`stopped: ${err.message}`); process.exitCode = 1; } finally { resyncing = false; } } function connect(lastSeq) { const ws = new OddsWebSocket({ apiKey, markets: [MARKET], leagues: [LEAGUE], status: 'live', lastSeq: lastSeq ?? undefined, }); feed = ws; // A closed feed can still deliver queued frames; only the current one may touch state. const on = (type, handler) => ws.on(type, (m) => ws === feed && handler(m)); on('welcome', (m) => { touched = new Set(); log(`connected, ${m.bookmakers.length} bookmakers on this key`); if (m.warning) log(`warning: ${m.warning}`); }); on('created', (m) => apply(m.id, m.bookie, m.markets)); on('updated', (m) => apply(m.id, m.bookie, m.markets)); on('deleted', (m) => apply(m.id, m.bookie, [])); on('no_markets', (m) => apply(m.id, m.bookie, [])); on('replay_complete', (m) => { if (m.outcome === 'live' && m.last_seq > 0) return resync('no catch-up sent'); if (m.outcome !== 'replayed' && m.outcome !== 'snapshot') return; if (m.outcome === 'snapshot') dropUntouched(); // Snapshot messages carry no seq, so move the resume point to where the catch-up ended. if (m.through_seq > (ws.lastSeq ?? 0)) ws.lastSeq = m.through_seq; log(`caught up (${m.outcome}), seq ${ws.lastSeq}`); }); on('resync_required', (m) => resync(m.reason)); on('reconnecting', ({ delay, lastSeq: seq }) => log(`disconnected, reconnecting in ${delay} ms from seq ${seq}`)); on('error', (err) => log(`error: ${err.message}`)); on('close', ({ willReconnect, code }) => { if (willReconnect) return; log(`stopped, connection closed (${code})`Source：https://dev.to/bjermeland/live-odds-api-in-nodejs-build-a-websocket-odds-tracker-2fi5
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