denoland/deno · error · TypeError

Referrer " " is not a valid URL.

Error message

Referrer "${referrer}" is not a valid URL.

What it means

When RequestInit.referrer is a non-empty string, the Request constructor parses it with new URL(referrer, baseURL). If parsing fails (the string is not an absolute URL and cannot be resolved against the current base — workers/scripts often have no base URL), the underlying SyntaxError is wrapped and re-thrown as TypeError 'Referrer "..." is not a valid URL.' with the original error as its cause.

Solutions

1. Pass an absolute URL: referrer: "https://example.com/source-page"
2. Pass "" for no referrer, or omit the option
3. Pre-validate with new URL(referrer) in a try/catch before constructing the Request

Example fix

// before
new Request("https://api.example.com/data", { referrer: "some page" }); // throws

// after
new Request("https://api.example.com/data", {
  referrer: "https://example.com/some-page",
});

let referrer;
if (init.referrer !== undefined && init.referrer !== "") {
  try {
    referrer = new URL(init.referrer).href; // must be absolute already
  } catch {
    referrer = undefined; // omit instead of throwing
  }
}
const req = new Request(url, { ...init, referrer });

function isAbsoluteUrl(s: string): boolean {
  try {
    new URL(s);
    return true;
  } catch {
    return false;
  }
}

try {
  new Request(url, { referrer });
} catch (err) {
  if (err instanceof TypeError && err.message.includes("not a valid URL")) {
    new Request(url, { referrer: "" }); // no-referrer fallback
  } else throw err;
}

When it happens

Trigger: new Request(url, { referrer: "not a url" }); referrer: "page.html" in a context without a location/base URL (worker, CLI script); referrer values containing spaces like "my page".

Common situations: Forwarding document.referrer or Referer headers verbatim into referrer; relative referrer strings that worked in a browser window (which has a base URL) but not in a Deno worker; typos in hardcoded referrers.

Related errors

• cannot read url: request closed
• Cannot read url: request closed
• Body is unusable
• Cannot read headers: request closed
• Input request's body is unusable

AI-assisted analysis of denoland/deno@9ad36f7a2c (2026-08-20). Data as JSON: /api/errors/21090e324149ff3e. Report an issue: GitHub.

Appendix: source

Thrown at ext/fetch/23_request.js:427

      // fold in of step 12 from below
      request = cloneInnerRequest(originalReq, true);
      request.redirectCount = 0; // reset to 0 - cloneInnerRequest copies the value
      signal = input[_signal];
    }

    // 12. is folded into the else statement of step 6 above.

    // 17. referrer
    if (init.referrer !== undefined) {
      const referrer = init.referrer;
      if (referrer === "") {
        request.referrer = "no-referrer";
      } else {
        let parsedReferrer;
        try {
          parsedReferrer = new URL(referrer, baseURL);
        } catch (err) {
          throw new TypeError(`Referrer "${referrer}" is not a valid URL.`, {
            cause: err,
          });
        }
        if (
          (parsedReferrer.protocol === "about:" &&
            parsedReferrer.pathname === "client")
        ) {
          request.referrer = "client";
        } else {
          request.referrer = parsedReferrer.href;
        }
      }
    }

    // 18. referrerPolicy
    if (init.referrerPolicy !== undefined) {
      request.referrerPolicy = init.referrerPolicy;
    }

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