mozilla/pdf.js · error · Error

Failed to fetch file "${url}" with "${response.statusText}".

Error message

Failed to fetch file "${url}" with "${response.statusText}".

What it means

Thrown by fetchBinaryData when the HTTP fetch resolves with response.ok === false. The helper is used internally to load .bcmap CMap files and standard-font metric files; the error message includes the URL and statusText so the missing asset is identifiable. It is a wrapper around the browser fetch() that turns non-2xx responses into exceptions.

Source

Thrown at src/core/core_utils.js:127

  }
  let dataLength = 0;
  for (let i = 0; i < length; i++) {
    dataLength += arr[i].byteLength;
  }
  const data = new Uint8Array(dataLength);
  let pos = 0;
  for (let i = 0; i < length; i++) {
    const item = new Uint8Array(arr[i]);
    data.set(item, pos);
    pos += item.byteLength;
  }
  return data;
}

async function fetchBinaryData(url) {
  const response = await fetch(url);
  if (!response.ok) {
    throw new Error(
      `Failed to fetch file "${url}" with "${response.statusText}".`
    );
  }
  return response.bytes();
}

/**
 * Get the value of an inheritable property.
 *
 * If the PDF specification explicitly lists a property in a dictionary as
 * inheritable, then the value of the property may be present in the dictionary
 * itself or in one or more parents of the dictionary.
 *
 * If the key is not found in the tree, `undefined` is returned. Otherwise,
 * the value for the key is returned or, if `stopWhenFound` is `false`, a list
 * of values is returned.
 *
 * @param {Dict} dict - Dictionary from where to start the traversal.

View on GitHub (pinned to 5903d58d58)

Solutions

1. Ship cmaps/ and standard_fonts/ from pdfjs-dist and set cMapUrl/standardFontDataUrl to their absolute, correctly-slash-terminated paths.
2. Verify each URL returns 200 in a browser devtools network panel (watch for 404 or CORS errors).
3. Serve the assets with permissive CORS headers if the worker origin differs from the asset origin.
4. If assets cannot be hosted at a URL, provide a custom fetchBuiltInCMap / standard-font loader that resolves them from local bytes.

Example fix

// before
getDocument({ url, cMapUrl: '/cmaps' }); // no trailing slash, packed unset

// after
getDocument({
  url,
  cMapUrl: '/assets/cmaps/',
  cMapPacked: true,
  standardFontDataUrl: '/assets/standard_fonts/',
});

// Probe asset URLs at app startup so a missing CMap/font fails fast and visibly
async function assertAssetOk(url) {
  const res = await fetch(url, { method: 'HEAD' });
  if (!res.ok) throw new Error(`Missing pdf.js asset: ${url} (${res.status})`);
}
await assertAssetOk(`${cMapUrl}78-RKSJ-H.bcmap`);

try {
  await loadingTask.promise;
} catch (e) {
  if (/Failed to fetch file/.test(e.message)) {
    console.error('CMap/standard-font asset unreachable - check cMapUrl/standardFontDataUrl/CORS', e);
  } else throw e;
}

When it happens

Trigger: getDocument configured with cMapUrl or standardFontDataUrl pointing at a path that returns 4xx/5xx (404 is most common); CORS preflight rejection; the asset server is down or returns an error status.

Common situations: Deployments that copy pdf.js/pdf.worker.js but forget to ship the cmaps/ and standard_fonts/ directories from pdfjs-dist; a wrong or missing trailing slash in cMapUrl; CORS blocking cross-origin asset fetches from the worker.

Related errors

• Unknown CMap name: ${name}
• Built-in CMap parameters are not provided.
• unexpected EOF in bcmap
• mapCidRange - ignoring data above MAX_MAP_RANGE.
• mapBfRange - ignoring data above MAX_MAP_RANGE.

AI-assisted analysis of mozilla/pdf.js@5903d58d58 (2026-08-13). Data as JSON: /api/errors/3085958d1edda3f4. Report an issue: GitHub.