grafana/k6 · error

options: expected string or object, got %T

Error message

options: expected string or object, got %T

What it means

Thrown by ConvertSelectOptionValues while iterating array items passed to selectOption (Page/Frame/Locator/ElementHandle). Each item must be either a string (matches value or label) or a plain object (common.SelectOption with value/label/index). Any other item type hits the default branch in browser/mapping.go:83 and aborts selection.

Solutions

1. Convert numeric items to strings before the call: values.map(String).
2. Wrap non-string items in an option object: { value: String(item) }.
3. Filter out null/undefined items: values.filter(v => v != null).
4. Validate each item with typeof before calling selectOption.

Example fix

// before
await page.selectOption('#size', data.sizes); // data.sizes = [1, 2, 3]

// after
await page.selectOption('#size', data.sizes.map(String));

const items = values.filter(v => v != null).map(v => typeof v === 'string' || typeof v === 'object' ? v : String(v));
await page.selectOption('#sel', items);

function isSelectOptionItem(i) {
  if (typeof i === 'string') return true;
  if (i == null || typeof i !== 'object' || Array.isArray(i)) return false;
  return Object.keys(i).every(k => ['value', 'label', 'index'].includes(k));
}

try { await page.selectOption('#sel', values); } catch (e) { if (/expected string or object/.test(e.message)) { /* map offending items to strings and retry */ } throw e; }

When it happens

Trigger: page.selectOption('#sel', [1, 2]) (numbers), [true] (booleans), [null] (nullish item), or [() => {}] (functions). Each array item must be 'red', { value: 'red' }, { label: 'Red' }, or { index: 2 }.

Common situations: Option lists read from a JSON data file where numeric values were not quoted (["1","2"] vs [1,2]); mixed arrays built by pushing DOM text that occasionally parses to a number; stale schema where the API started returning integers for option values.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• options: expected array, got %T
• options: expected object, got %T
• options: unsupported type %T
• options[ ]: expected int, got %T
• options[ ]: expected string, got %T

AI-assisted analysis of grafana/k6@8d06114777 (2026-08-18). Data as JSON: /api/errors/0ac4220db25bd658. Report an issue: GitHub.

Appendix: source

Thrown at internal/js/modules/k6/browser/browser/mapping.go:91

		for _, item := range sl {
			switch item := item.(type) {
			case string:
				// Strings will match values or labels
				valOpt := common.SelectOption{Value: new(string)}
				*valOpt.Value = item
				labelOpt := common.SelectOption{Label: new(string)}
				*labelOpt.Label = item
				opts = append(opts, &valOpt, &labelOpt)
			case map[string]any:
				opt, err := extractSelectOptionFromMap(item)
				if err != nil {
					return nil, err
				}

				opts = append(opts, opt)
			default:
				return nil, fmt.Errorf("options: expected string or object, got %T", item)
			}
		}
	case reflect.Map:
		var raw map[string]any
		if err := rt.ExportTo(values, &raw); err != nil {
			return nil, fmt.Errorf("options: expected object, got %T", values)
		}

		opt, err := extractSelectOptionFromMap(raw)
		if err != nil {
			return nil, err
		}

		opts = append(opts, opt)
	case reflect.TypeFor[*common.ElementHandle]().Kind():
		opts = append(opts, t.(*common.ElementHandle)) //nolint:forcetypeassert
	case reflect.TypeFor[sobek.Object]().Kind():
		obj := values.ToObject(rt)

View on GitHub (pinned to 8d06114777)