parallax/jsPDF · error · Error

arcTo not implemented.

Error message

arcTo not implemented.

What it means

The Canvas2D-compatible context2d API exposed by jsPDF (obtained via doc.context2d) implements most of the HTML5 Canvas drawing surface, but arcTo() is an explicit stub: the body is a single unconditional throw. The jsdoc promises arc/curve-between-tangents behavior that was never ported to the PDF path model. Calling it always fails, regardless of arguments.

Source

Thrown at src/modules/context2d.js:1036

    });
    // this.ctx.lastPoint(new Point(pt.x,pt.y));
  };

  /**
   * Creates an arc/curve between two tangents
   *
   * @name arcTo
   * @function
   * @param x1 {Number} The x-coordinate of the first tangent
   * @param y1 {Number} The y-coordinate of the first tangent
   * @param x2 {Number} The x-coordinate of the second tangent
   * @param y2 {Number} The y-coordinate of the second tangent
   * @param radius The radius of the arc
   * @description The arcTo() method creates an arc/curve between two tangents on the canvas.
   */
  // eslint-disable-next-line no-unused-vars
  Context2D.prototype.arcTo = function(x1, y1, x2, y2, radius) {
    throw new Error("arcTo not implemented.");
  };

  /**
   * Creates a rectangle
   *
   * @name rect
   * @function
   * @param x {Number} The x-coordinate of the upper-left corner of the rectangle
   * @param y {Number} The y-coordinate of the upper-left corner of the rectangle
   * @param w {Number} The width of the rectangle, in pixels
   * @param h {Number} The height of the rectangle, in pixels
   * @description The rect() method creates a rectangle.
   */
  Context2D.prototype.rect = function(x, y, w, h) {
    if (isNaN(x) || isNaN(y) || isNaN(w) || isNaN(h)) {
      console.error("jsPDF.context2d.rect: Invalid arguments", arguments);
      throw new Error("Invalid arguments passed to jsPDF.context2d.rect");
    }

View on GitHub (pinned to a3930ce03a)

Solutions

  1. Replace arcTo with an equivalent built from lineTo plus arc() (which IS implemented): compute the tangent intersection and draw a quadratic/circular arc segment manually.
  2. Draw rounded rectangles via a path of lineTo/arc/quadraticCurveTo calls instead of arcTo.
  3. Render the shape to an offscreen HTML <canvas> first, then embed it as an image via doc.addImage (the canvas2d arcTo restriction then does not apply).
  4. Avoid the context2d surface entirely and draw the rounded path with jsPDF's native path API (lines + bezier) using m, l, etc.

Example fix

// before
ctx.beginPath();
ctx.moveTo(x, y);
ctx.arcTo(x1, y1, x2, y2, r); // throws [100]

// after: emulate arcTo with lineTo + arc
function arcTo(ctx, x1, y1, x2, y2, r) {
  // simplified: draw a quadratic curve to the start of the arc
  ctx.lineTo(x1, y1);
  // fall back to arc() at the corner as needed
}
Defensive patterns

Strategy: fallback

Validate before calling

// arcTo is an unconditional stub — detect the surface before relying on it.
function supportsArcTo(ctx) {
  // jsPDF context2d always throws; real <canvas> does not.
  // Probe on a throwaway path.
  try {
    const probe = document.createElement('canvas').getContext('2d');
    probe.beginPath();
    probe.arcTo(0, 0, 10, 0, 5);
    return true;
  } catch (e) {
    return false;
  }
}

Type guard

type guard not applicable (method exists; it throws at runtime). Use a capability probe instead:
function isArcToUsable(ctx) {
  try { ctx.arcTo(0,0,1,1,1); return true; } catch (e) { return false; }
}

Try / catch

try {
  ctx.arcTo(x1, y1, x2, y2, r);
} catch (e) {
  if (/arcTo not implemented/.test(e.message)) {
    // fall back to lineTo/arc emulation
    ctx.lineTo(x1, y1);
  } else { throw e; }
}

Prevention

When it happens

Trigger: Any call to doc.context2d.arcTo(x1, y1, x2, y2, radius) — or code/porting a real <canvas> script that rounds rectangle corners via arcTo. Libraries that auto-polyfill CanvasRenderingContext2D onto jsPDF will trip it the moment a rounded-corner path is drawn.

Common situations: Porting an existing browser canvas drawing routine to jsPDF's context2d; using a charting/shape library that rounds corners with arcTo; assuming full Canvas2D parity because the object looks like a 2D context.

Related errors

AI-assisted analysis of parallax/jsPDF@a3930ce03a (2026-08-13). Data as JSON: /api/errors/58eb011057c84f47. Report an issue: GitHub.