mozilla/pdf.js · error · Error

Invalid factory url: "${val}" must include trailing slash.

Error message

Invalid factory url: "${val}" must include trailing slash.

What it means

Thrown by getFactoryUrlProp when a configured cMapUrl, standardFontDataUrl, or wasmUrl is a string that does not end with '/'. PDF.js builds resource URLs via simple concatenation (baseUrl + filename), so a missing trailing slash produces paths like 'https://x/cmaps' + 'JP' rather than 'https://x/cmaps/JP', silently breaking CJK/font/WASM fetching. The check makes this a hard error instead.

Source

Thrown at src/display/api_utils.js:98

    ArrayBuffer.isView(val) ||
    (typeof val === "object" && !isNaN(val?.length))
  ) {
    return new Uint8Array(val);
  }
  throw new Error(
    "Invalid PDF binary data: either TypedArray, " +
      "string, or array-like object is expected in the data property."
  );
}

function getFactoryUrlProp(val) {
  if (typeof val !== "string") {
    return null;
  }
  if (val.endsWith("/")) {
    return val;
  }
  throw new Error(`Invalid factory url: "${val}" must include trailing slash.`);
}

const isRefProxy = v =>
  typeof v === "object" &&
  Number.isInteger(v?.num) &&
  v.num >= 0 &&
  Number.isInteger(v?.gen) &&
  v.gen >= 0;

const isNameProxy = v => typeof v === "object" && typeof v?.name === "string";

const isValidExplicitDest = _isValidExplicitDest.bind(
  null,
  /* validRef = */ isRefProxy,
  /* validName = */ isNameProxy
);

class LoopbackPort {

View on GitHub (pinned to 5903d58d58)

Solutions

Append '/' to the configured URL: cMapUrl: 'https://cdn.example.com/cmaps/'.
Normalize at config time: const withSlash = url.endsWith('/') ? url : url + '/'.
Verify the same for standardFontDataUrl and wasmUrl when used.

Example fix

// before
getDocument({ data, cMapUrl: 'https://cdn.example.com/cmaps' });

// after
getDocument({ data, cMapUrl: 'https://cdn.example.com/cmaps/' });

Defensive patterns

Strategy: validation

Validate before calling

function ensureTrailingSlash(u) {
  return typeof u === 'string' && !u.endsWith('/') ? u + '/' : u;
}
getDocument({
  data,
  cMapUrl: ensureTrailingSlash(config.cMapUrl),
  standardFontDataUrl: ensureTrailingSlash(config.standardFontDataUrl),
});

Type guard

null

Try / catch

null

Prevention

Normalize every factory URL with a trailing slash at config build time.
Keep config in one place so the rule is applied uniformly.
Add a CI check that asserts these URLs end with '/'.

When it happens

Trigger: Passing getDocument({ cMapUrl: 'https://cdn.example/cmaps' }), or any of the three factory URLs without the closing slash.

Common situations: Copy-pasting a base URL from a hosting panel that strips trailing slashes; switching from a version of pdfjs that auto-appended '/' to one that does not; CDN config that canonicalizes URLs without slashes.

Related errors

AI-assisted analysis of mozilla/pdf.js@5903d58d58 (2026-08-13). Data as JSON: /api/errors/d44150d472223bd2. Report an issue: GitHub.