denoland/deno · error · TypeError

Invalid port: ''

Error message

Invalid port: ''

What it means

An empty-string port is rejected outright with TypeError("Invalid port: ''"). The dedicated check exists because Number("") === 0, which would otherwise silently bind or connect to port 0 — an OS-assigned or invalid target — instead of surfacing the missing value as an error.

Solutions

1. Default falsy to a concrete port: const port = Number(Deno.env.get("PORT") || 3000).
2. For URLs, fall back to the scheme default: url.port || (url.protocol === "https:" ? "443" : "80").
3. Validate config at startup and fail fast with a clear message before any socket call.

Example fix

// before
const port = Deno.env.get("PORT") ?? ""; // PORT defined but empty
Deno.listen({ port }); // Invalid port: ''

// after
const port = Number(Deno.env.get("PORT") || 3000);
Deno.listen({ port });

const envPort = Deno.env.get("PORT");
const port = Number(envPort && envPort.trim() !== "" ? envPort : 3000);
if (!Number.isInteger(port) || port < 1 || port > 65535) {
  throw new Error(`invalid PORT configuration: ${JSON.stringify(envPort)}`);
}

const isNonEmptyPortString = (v: unknown): v is string =>
  typeof v === "string" && v.trim() !== "" && Number.isInteger(Number(v));

When it happens

Trigger: `port: Deno.env.get("PORT")` when PORT is set but empty; `new URL("https://example.com/").port` which is "" when the URL carries no explicit port; splitting "host:" on ":"; template `${cfg.port}` when cfg.port is an empty string.

Common situations: PORT env var defined-but-empty in .env files or CI variable passthrough; URLs without ports where the scheme default was expected; config merges that leave "" instead of undefined.

Related errors

• Invalid port (expected number)
• Invalid port
• EPIPE
• ERR_INVALID_ARG_TYPE
• ERR_INVALID_ARG_VALUE

AI-assisted analysis of denoland/deno@9ad36f7a2c (2026-08-20). Data as JSON: /api/errors/0928a6e5d265919f. Report an issue: GitHub.

Appendix: source

Thrown at ext/net/01_net.js:647

      const { 0: rid, 1: addr } = op_net_listen_tunnel();
      return new Listener(rid, addr, "tunnel");
    }
    default:
      throw new TypeError(`Unsupported transport: '${transport}'`);
  }
}

function validatePort(maybePort, isServer = false) {
  // A missing port means "any available port" (port 0) for servers. Clients
  // must always specify a port to connect to, so a missing port is left as-is
  // and rejected below.
  if (isServer && (maybePort === null || maybePort === undefined)) {
    maybePort = 0;
  }
  if (typeof maybePort !== "number" && typeof maybePort !== "string") {
    throw new TypeError(`Invalid port (expected number): ${maybePort}`);
  }
  if (maybePort === "") throw new TypeError("Invalid port: ''");
  const port = Number(maybePort);
  if (!NumberIsInteger(port)) {
    if (NumberIsNaN(port) && !NumberIsNaN(maybePort)) {
      throw new TypeError(`Invalid port: '${maybePort}'`);
    } else {
      throw new TypeError(`Invalid port: ${maybePort}`);
    }
  } else if (port < (isServer ? 0 : 1) || port > 65535) {
    // Servers may bind to port 0 (OS-assigned), clients may not connect to it.
    throw new RangeError(`Invalid port (out of range): ${maybePort}`);
  }
  return port;
}

function createListenDatagram(udpOpFn, unixOpFn) {
  return function listenDatagram(args) {
    switch (args.transport) {
      case "udp": {

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