mozilla/pdf.js · error · Error

doc.pageWindowRect is read-only

Error message

doc.pageWindowRect is read-only

What it means

`Doc.pageWindowRect` returns `[left, top, right, bottom]` describing the page window rectangle. PDF.js returns `[0,0,0,0]` (browser viewer has no such windowing concept). It is read-only by the Acrobat spec, and the throwing setter rejects scripts that try to set it.

Source

Thrown at src/scripting_api/doc.js:583

  set pageNum(value) {
    if (!this._userActivation) {
      return;
    }
    this._userActivation = false;

    if (typeof value !== "number" || value < 0 || value >= this._numPages) {
      return;
    }
    this._send({ command: "page-num", value });
    this._pageNum = value;
  }

  get pageWindowRect() {
    return [0, 0, 0, 0];
  }

  set pageWindowRect(_) {
    throw new Error("doc.pageWindowRect is read-only");
  }

  get path() {
    return "";
  }

  set path(_) {
    throw new Error("doc.path is read-only");
  }

  get permStatusReady() {
    return true;
  }

  set permStatusReady(_) {
    throw new Error("doc.permStatusReady is read-only");
  }

View on GitHub (pinned to 5903d58d58)

Solutions

  1. Drop the assignment — the value is read-only and constant `[0,0,0,0]` in PDF.js.
  2. Use viewer-level zoom/layout controls to affect page display instead.
  3. Run untrusted scripts through a try/catch boundary.

Example fix

// before
doc.pageWindowRect = [0, 0, 612, 792];

// after
// (remove) — read-only; returns [0,0,0,0] in PDF.js
Defensive patterns

Strategy: try-catch

Validate before calling

const READ_ONLY_DOC_PROPS = new Set(['pageWindowRect','outerAppWindowRect' /* ... */]);
function assertsNoReadOnlyWrite(scriptSrc) {
  for (const p of READ_ONLY_DOC_PROPS) {
    if (new RegExp(`\\bdoc\\.${p}\\s*=[^=]`).test(scriptSrc)) {
      throw new Error(`Script writes read-only property doc.${p}`);
    }
  }
}
assertsNoReadOnlyWrite(myScript);

Type guard

function isReadOnlyDocProp(doc, prop) {
  const desc = Object.getOwnPropertyDescriptor(Object.getPrototypeOf(doc), prop)
    || Object.getOwnPropertyDescriptor(doc, prop);
  return !!desc && !!desc.get && !desc.set;
}
isReadOnlyDocProp(doc, 'pageWindowRect'); // true

Try / catch

try {
  doc.pageWindowRect = [0,0,612,792];
} catch (e) {
  if (/pageWindowRect is read-only/.test(e.message)) console.warn(e.message);
  else throw e;
}

Prevention

When it happens

Trigger: A script assigns to `doc.pageWindowRect` (e.g. `doc.pageWindowRect = [0,0,500,500];`). The setter throws at that line.

Common situations: Scripts targeting desktop Acrobat windowing; layout/snapshot scripts; code blindly probing all properties.

Related errors

AI-assisted analysis of mozilla/pdf.js@5903d58d58 (2026-08-13). Data as JSON: /api/errors/35518e74456c0c2f. Report an issue: GitHub.