grafana/k6 · error

options[ ]: expected string, got %T

Error message

options[%v]: expected string, got %T

What it means

Thrown by extractSelectOptionFromMap (browser/mapping.go:140) while parsing a selectOption descriptor object: the 'value' key was present but its value is not a string. k6 requires value-based selection descriptors to be { value: '<string>' }; the type assertion raw.(string) fails for any other Go export type and the offending key name is included in the message.

Solutions

1. Quote the value: { value: '123' } or { value: String(optionValue) }.
2. Coerce at the data boundary: options = rawOptions.map(o => ({ ...o, value: String(o.value) })).
3. If the option genuinely has no value attribute, match by label ({ label: '...' }) or index ({ index: n }) instead.
4. Add a runtime check that every descriptor's value field is typeof 'string'.

Example fix

// before
await page.selectOption('#sel', { value: data.userId }); // userId = 1001

// after
await page.selectOption('#sel', { value: String(data.userId) });

const opt = { ...raw };
if ('value' in opt && typeof opt.value !== 'string') opt.value = String(opt.value);
await page.selectOption('#sel', opt);

function hasStringValue(o) {
  return !('value' in o) || typeof o.value === 'string';
}

try { await page.selectOption('#sel', opt); } catch (e) { if (/options\[value\]: expected string/.test(e.message)) { await page.selectOption('#sel', { ...opt, value: String(opt.value) }); } else throw e; }

When it happens

Trigger: page.selectOption('#sel', { value: 123 }), { value: true }, or { value: null }. Numeric option values read from JSON without string conversion are the classic case.

Common situations: Option values sourced from a JSON/CSV dataset where values are numbers; APIs that return option values as integers; shared option objects reused from URL query building where numbers are common.

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

AI-assisted analysis of grafana/k6@8d06114777 (2026-08-18). Data as JSON: /api/errors/04f010d0bc7f37cf. Report an issue: GitHub.

Appendix: source

Thrown at internal/js/modules/k6/browser/browser/mapping.go:148

		*labelOpt.Label = t.(string) //nolint:forcetypeassert
		opts = append(opts, &valOpt, &labelOpt)
	default:
		return nil, fmt.Errorf("options: unsupported type %T", values)
	}

	return opts, nil
}

func extractSelectOptionFromMap(v map[string]any) (*common.SelectOption, error) {
	opt := &common.SelectOption{}
	for k, raw := range v {
		switch k {
		case "value":
			opt.Value = new(string)

			v, ok := raw.(string)
			if !ok {
				return nil, fmt.Errorf("options[%v]: expected string, got %T", k, raw)
			}

			*opt.Value = v
		case "label":
			opt.Label = new(string)

			v, ok := raw.(string)
			if !ok {
				return nil, fmt.Errorf("options[%v]: expected string, got %T", k, raw)
			}
			*opt.Label = v
		case "index":
			opt.Index = new(int64)

			switch raw := raw.(type) {
			case int:
				*opt.Index = int64(raw)
			case int64:

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