What causes "converting result (%v of type %t) to border: %w" in grafana/k6?

Ensure the element is rendered and laid out before using a pos offset: await el.waitFor({ state: 'visible' })

converting result ( of type %t) to border

Error message

converting result (%v of type %t) to border: %w

What it means

offsetPosition() runs the injected getElementBorderWidth script and converts the result to a {Top, Left float64} border struct; convert() failed, meaning the JS returned something unconvertible (null, strings, or a differently-shaped object). Note the message itself has a formatting bug: %t is applied to a non-bool value, so the type prints as %!t(...) garbage.

Solutions

Ensure the element is rendered and laid out before using a pos offset: await el.waitFor({ state: 'visible' })
Prefer plain click() (center of the element) when you don't truly need an offset
If an offset is required, verify the element's border style is computable (not display:none, not detached shadow DOM)
File a k6 issue about the garbled %t formatting so the real type is logged

Example fix

// before
await el.click({ pos: { x: 10, y: 10 } }); // element hidden

// after
await el.waitFor({ state: 'visible' });
await el.click(); // center click, no offset conversion needed

Defensive patterns

Strategy: validation

Validate before calling

// only use pos offsets on laid-out, visible standard elements
await el.waitFor({ state: 'visible' });
const box = await el.boundingBox();
if (!box) throw new Error('element not laid out; skip pos offset');

Try / catch

try {
  await el.click({ pos: { x: 5, y: 5 } });
} catch (e) {
  if (/to border/.test(String(e))) {
    await el.click(); // fall back to center click
  } else throw e;
}

Prevention

Avoid pos offsets on custom elements and closed shadow DOM
Ensure elements are rendered before offset-based clicks

When it happens

Trigger: Using click({ pos: { x, y } }) / pointer options with an offset on an element where getElementBorderWidth returns null or a non-numeric shape: custom elements, elements whose computed style is unavailable (in a detached shadow root or display:none), or pages stubbing getComputedStyle.

Common situations: Clicking by offset on custom web components or elements in closed shadow DOM; offset clicks on elements that are not yet laid out; k6 versions before the offset path was hardened — the mangled %t output makes logs confusing regardless of cause.

Related errors

AI-assisted analysis of grafana/k6@3fcf5388d7 (2026-08-18). Data as JSON: /api/errors/06e7ef780ba77672. Report an issue: GitHub.

Appendix: source

Thrown at internal/js/modules/k6/browser/common/element_handle.go:438

func (h *ElementHandle) offsetPosition(apiCtx context.Context, offset *Position) (*Position, error) {
	fn := `
		(node, injected) => {
			return injected.getElementBorderWidth(node);
		}
	`
	opts := evalOptions{
		forceCallable: true,
		returnByValue: true,
	}
	result, err := h.evalWithScript(apiCtx, opts, fn)
	if err != nil {
		return nil, err
	}

	var border struct{ Top, Left float64 }
	if err := convert(result, &border); err != nil {
		return nil, fmt.Errorf("converting result (%v of type %t) to border: %w", result, result, err)
	}

	box, err := h.BoundingBox()
	if err != nil {
		return nil, fmt.Errorf("finding offset position: %w", err)
	}

	if box == nil || (border.Left == 0 && border.Top == 0) {
		return nil, ErrElementNotVisible
	}

	// Make point relative to the padding box to align with offsetX/offsetY.
	return &Position{
		X: box.X + border.Left + offset.X,
		Y: box.Y + border.Top + offset.Y,
	}, nil
}

View on GitHub (pinned to 3fcf5388d7)