mozilla/pdf.js · error · Error

extractPages: overlapping pageIndices.

Error message

extractPages: overlapping pageIndices.

What it means

Plain Error thrown by reservePageSlot when a newPageIndex is already occupied in this.oldPages (slot !== undefined). It prevents two source pages from being written to the same output slot, which would silently lose data.

Source

Thrown at src/core/editor/pdf_editor.js:994

   * @return {Promise<void>}
   */
  async extractPages(
    pageInfos,
    annotationStorage,
    primaryDocument,
    handler,
    task
  ) {
    this.#primaryDocument = primaryDocument;
    pageInfos = this.#resolveInsertAfterIndices(pageInfos);
    const promises = [];
    let newIndex = 0;
    const reservePageSlot = newPageIndex => {
      if (!Number.isInteger(newPageIndex) || newPageIndex < 0) {
        throw new Error("extractPages: invalid page index.");
      }
      if (this.oldPages[newPageIndex] !== undefined) {
        throw new Error("extractPages: overlapping pageIndices.");
      }
      // Reserve the slot immediately because page/image collection can be
      // async.
      this.oldPages[newPageIndex] = null;
    };
    const allDocumentData = [];

    if (annotationStorage) {
      this.#newAnnotationsParams = {
        handler,
        task,
        newAnnotationsByPage: getNewAnnotationsMap(annotationStorage),
        imagesPromises: AnnotationFactory.generateImages(
          annotationStorage.values(),
          this.xrefWrapper,
          true
        ),
      };

View on GitHub (pinned to 5903d58d58)

Solutions

1. De-duplicate all pageIndices across pageInfos before calling extractPages.
2. After resolving insertAfter yourself, ensure no slot is referenced twice.
3. Compute target slots programmatically (e.g., accumulate an offset) rather than hard-coding.

Example fix

// before
pageInfos = [
  { document: a, pageIndices: [0, 2] },
  { document: b, pageIndices: [2, 4] },   // '2' overlaps
];

// after
pageInfos = [
  { document: a, pageIndices: [0, 2] },
  { document: b, pageIndices: [3, 4] },
];

function assertNoOverlap(pageInfos) {
  const seen = new Set();
  for (const p of pageInfos) {
    for (const idx of p.pageIndices ?? []) {
      if (seen.has(idx)) throw new Error(`Overlapping pageIndex: ${idx}`);
      seen.add(idx);
    }
  }
}

try {
  await editor.extractPages(pageInfos, ...);
} catch (e) {
  if (e.message === 'extractPages: overlapping pageIndices.') {
    pageInfos = dedupeSlots(pageInfos);
    return editor.extractPages(pageInfos, ...);
  }
  throw e;
}

When it happens

Trigger: pageIndices across multiple pageInfos that share a value (e.g., both [{pageIndices:[2]}] and [{pageIndices:[2]}]); a single pageInfo with duplicate pageIndices; an insertAfter resolution that collides with explicit pageIndices.

Common situations: Caller reuses pageIndices from different sources without de-duplication; off-by-one when manually shifting indices after an insert.

Related errors

• extractPages: invalid page index.
• extractPages: sparse pageIndices.
• extractPages: partial pageIndices cannot be combined with in
• extractPages: too many pageIndices.
• extractPages: nothing to extract.

AI-assisted analysis of mozilla/pdf.js@5903d58d58 (2026-08-13). Data as JSON: /api/errors/44af86c90ce572e4. Report an issue: GitHub.