antonmedv/fx · error

Unsupported value type

Error message

Unsupported value type: %v

What it means

Terminal panic in Stringify: the goja value's reflected kind is none of the supported types (object/array/etc.), so no JSON rendering branch applies. In practice it fires for exotic or uninitialized reflected values reaching the printer, indicating an unsupported value rather than malformed user JSON.

Solutions

1. Avoid piping values of the unsupported type into Stringify
2. Convert the value to a plain object/array/string before printing
3. Extend Stringify with a branch for the reported reflect.Kind

When it happens

Trigger: Thrown at internal/engine/stringify.go:112 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of antonmedv/fx@4f31cd3a0c (2026-09-02). Data as JSON: /api/errors/334f1a5999187918. Report an issue: GitHub.

Appendix: source

Thrown at internal/engine/stringify.go:112

		var out strings.Builder
		out.WriteString("[")
		out.WriteString("\n")

		for i, key := range keys {
			item := arr.Get(key)
			out.WriteString(strings.Repeat("  ", depth+1))
			out.WriteString(Stringify(item, vm, depth+1))
			if i < len(keys)-1 {
				out.WriteString(",")
			}
			out.WriteString("\n")
		}

		out.WriteString(strings.Repeat("  ", depth))
		out.WriteString("]")
		return out.String()
	}
	panic(fmt.Sprintf("Unsupported value type: %v", rtype.Kind()))
}

View on GitHub (pinned to 4f31cd3a0c)