mozilla/pdf.js · error · FormatError

Unknown function type: ${typeNum}

Error message

Unknown function type: ${typeNum}

What it means

Thrown by PDFFunctionFactory when a PDF function dictionary's /FunctionType is not one of the four supported values (0=SAMPLED, 2=EXPONENTIAL_INTERPOLATION, 3=STITCHING, 4=POSTSCRIPT_CALCULATOR). The switch in PDFFunction.parse falls through and aborts construction of the function object, which PDF.js uses for gradients, color mappings, and transfer functions.

Source

Thrown at src/core/function.js:145

    }
    return array;
  }

  static parse(factory, fn) {
    const dict = fn.dict || fn;
    const typeNum = dict.get("FunctionType");

    switch (typeNum) {
      case FunctionType.SAMPLED:
        return this.constructSampled(factory, fn, dict);
      case FunctionType.EXPONENTIAL_INTERPOLATION:
        return this.constructInterpolated(factory, dict);
      case FunctionType.STITCHING:
        return this.constructStiched(factory, dict);
      case FunctionType.POSTSCRIPT_CALCULATOR:
        return this.constructPostScript(factory, fn, dict);
    }
    throw new FormatError(`Unknown function type: ${typeNum}`);
  }

  static parseArray(factory, fnObj) {
    const { xref } = factory;

    const fnArray = [];
    for (const fn of fnObj) {
      fnArray.push(this.parse(factory, xref.fetchIfRef(fn)));
    }
    return function (src, srcOffset, dest, destOffset) {
      for (let i = 0, ii = fnArray.length; i < ii; i++) {
        fnArray[i](src, srcOffset, dest, destOffset + i);
      }
    };
  }

  static constructSampled(factory, fn, dict) {
    // See chapter 3, page 109 of the PDF reference

View on GitHub (pinned to 5903d58d58)

Solutions

1. Confirm the PDF is valid by opening it in Acrobat; if it renders there, attach the file to a pdf.js issue since the parser may need to tolerate the value.
2. If you control the PDF generation, ensure every function object sets /FunctionType to 0, 2, 3, or 4 per PDF 32000-1 §7.10.
3. Wrap page rendering in a try/catch and degrade gracefully (skip the offending annotation/shading) rather than aborting the whole render.
4. Pre-validate with a PDF/A conformance checker which flags non-standard function types.

Example fix

// before: rendering a page aborts on a bad function type
await page.render({ canvasContext }).promise;

// after: tolerate per-shading failures
try {
  await page.render({ canvasContext }).promise;
} catch (err) {
  if (err?.message?.startsWith('Unknown function type:')) {
    console.warn('Skipping page with unsupported PDF function:', err.message);
  } else throw err;
}

// No public pre-check exists; PDFFunctionFactory is internal to the worker.
// If you parse PDFs yourself, validate before passing to pdf.js:
function isValidFunctionType(dict) {
  const t = dict.get('FunctionType');
  return [0, 2, 3, 4].includes(t);
}

function isKnownFunctionType(typeNum) {
  return typeNum === 0 || typeNum === 2 || typeNum === 3 || typeNum === 4;
}

try {
  await page.render({ canvasContext }).promise;
} catch (err) {
  if (err?.message?.startsWith('Unknown function type:')) {
    console.warn('Unsupported PDF function type; skipping page.');
  } else throw err;
}

When it happens

Trigger: A PDF contains a function stream/dict whose FunctionType entry is missing, null, undefined, or any integer other than 0/2/3/4 (e.g. 1, 5, or a non-integer). Reached via getDocument() rendering of any page using shading patterns, Indexed color spaces with lookup functions, or halftone/transfer functions.

Common situations: Encountered with malformed or writer-buggy PDFs that emit a reserved/invalid function type, or with PDFs that omit /FunctionType entirely. Also seen when a corrupt xref causes dict.get('FunctionType') to resolve to garbage.

Related errors

• No domain or range
• No domain
• No domain.
• No shading resource found
• No shading object found

AI-assisted analysis of mozilla/pdf.js@5903d58d58 (2026-08-13). Data as JSON: /api/errors/691ad4084efe3805. Report an issue: GitHub.