Node.js: How do you implement a custom connection pool for WebSocket connections?

1const WebSocket = require("ws");
2
3class WebSocketPool {
4    constructor(urls, options = {}) {
5        this.urls = urls;
6        this.maxSize = options.maxSize || urls.length;
7        this.connections = [];
8        this.available = [];
9        this.currentIndex = 0;
10    }
11
12    async connect() {
13        for (const url of this.urls.slice(0, this.maxSize)) {
14            const ws = new WebSocket(url);
15            await new Promise((resolve, reject) => {
16                ws.on("open", () => {
17                    this.connections.push(ws);
18                    this.available.push(ws);
19                    resolve();
20                });
21                ws.on("error", reject);
22            });
23        }
24    }
25
26    getConnection() {
27        if (this.available.length === 0) {
28            throw new Error("No available connections");
29        }
30        // Round-robin
31        const ws = this.available.shift();
32        return ws;
33    }
34
35    release(ws) {
36        if (ws.readyState === WebSocket.OPEN) {
37            this.available.push(ws);
38        }
39    }
40
41    async send(data) {
42        const ws = this.getConnection();
43        try {
44            return await new Promise((resolve, reject) => {
45                ws.send(data, (err) => {
46                    if (err) reject(err);
47                    else resolve();
48                });
49            });
50        } finally {
51            this.release(ws);
52        }
53    }
54
55    close() {
56        this.connections.forEach(ws => ws.close());
57        this.connections = [];
58        this.available = [];
59    }
60}
61
62// Usage
63const pool = new WebSocketPool([
64    "ws://server1:8080",
65    "ws://server2:8080",
66    "ws://server3:8080",
67]);
68await pool.connect();
69await pool.send(JSON.stringify({ type: "ping" }));