mozilla/pdf.js · error · Error

Invalid rotation: must be a multiple of 90

Error message

Invalid rotation: must be a multiple of 90

What it means

Thrown by the setter of `Field.rotation` (src/scripting_api/field.js:212). A field's rotation must be a whole-number multiple of 90 degrees (0, 90, 180, 270) to align with the PDF coordinate system. The setter floors the value first, then rejects anything not divisible by 90.

Solutions

1. Quantize the angle before assigning: `f.rotation = Math.round(angle / 90) * 90`.
2. Ensure the source value is in degrees, not radians (`angle * 180 / Math.PI`).
3. Floor explicitly and assert divisibility before the call to give a clearer error.

Example fix

// before
f.rotation = degrees;
// after
f.rotation = Math.round(degrees / 90) * 90; // 0, 90, 180, 270

function setRotationSafe(field, angle) {
  const deg = Math.round(Number(angle) / 90) * 90;
  if (!Number.isFinite(deg)) return false;
  field.rotation = deg;
  return true;
}

function isQuantized90(v) {
  const n = Math.floor(Number(v));
  return Number.isFinite(n) && n % 90 === 0;
}

When it happens

Trigger: Assigning `f.rotation = 45`, `f.rotation = 12.5`, or a computed angle from `Math.atan2(...)` that is not quantized to 90. Passing a value in radians by mistake.

Common situations: Scripts that rotate a field to match a diagonal line or an image angle; reading a rotation out of an annotation whose value was never quantized; off-by-one on a UI slider that snaps to 1-degree steps.

Related errors

• field.numItems is read-only
• field.page is read-only
• Invalid argument value
• Invalid number of params in printf
• Not a choice widget

AI-assisted analysis of mozilla/pdf.js@5903d58d58 (2026-08-13). Data as JSON: /api/errors/4b455c3e861618a5. Report an issue: GitHub.

Appendix: source

Thrown at src/scripting_api/field.js:212

    this.strokeColor = color;
  }

  get page() {
    return this._page;
  }

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

  get rotation() {
    return this._rotation;
  }

  set rotation(angle) {
    angle = Math.floor(angle);
    if (angle % 90 !== 0) {
      throw new Error("Invalid rotation: must be a multiple of 90");
    }
    angle %= 360;
    if (angle < 0) {
      angle += 360;
    }
    this._rotation = angle;
  }

  get textColor() {
    return this._textColor;
  }

  set textColor(color) {
    if (Color._isValidColor(color)) {
      this._textColor = color;
    }
  }

View on GitHub (pinned to 5903d58d58)