elsa-workflows/elsa-core · error · InvalidOperationException

Unsupported JsonValueKind

Error message

Unsupported JsonValueKind: {element.ValueKind}

What it means

JsonElementConverter maps a System.Text.Json JsonElement to a Jint JsValue, handling Object, Array, String, Number, True, False, Undefined, and Null kinds. Any other JsonValueKind (e.g. certain document-root or exotic kinds surfaced by newer parsers) has no mapping and throws this InvalidOperationException. It marks an unhandled JSON element shape in the JavaScript expression bridge.

Solutions

1. Ensure the JsonElement is fully materialized (use JsonDocument.Parse(...).RootElement or Clone()) before conversion
2. Check element.ValueKind before calling and normalize unsupported kinds to Object/Null
3. Inspect the value's ValueKind at the failing point and fix the producer of the JSON
4. Extend JsonElementConverter.ConvertJsonElementToJsValue with a mapping for the missing kind

Example fix

// before
JsValue v = converter.Convert(jsonDoc.RootElement); // kind not handled
// after
using var doc = JsonDocument.Parse(json);
var element = doc.RootElement.Clone(); // materialized Object/Array/String/Number
JsValue v = converter.Convert(element);

bool IsSupportedKind(JsonElement e) => e.ValueKind is JsonValueKind.Object or JsonValueKind.Array
    or JsonValueKind.String or JsonValueKind.Number
    or JsonValueKind.True or JsonValueKind.False
    or JsonValueKind.Undefined or JsonValueKind.Null;
if (!IsSupportedKind(element)) throw new InvalidOperationException($"Unsupported JsonValueKind: {element.ValueKind}");

static bool IsConvertibleToJsonValue(JsonElement element) =>
    element.ValueKind is not (JsonValueKind.Object or JsonValueKind.Array or JsonValueKind.String
        or JsonValueKind.Number or JsonValueKind.True or JsonValueKind.False
        or JsonValueKind.Undefined or JsonValueKind.Null) is false;

try { jsValue = converter.ConvertJsonElementToJsValue(element); }
catch (InvalidOperationException ex) when (ex.Message.StartsWith("Unsupported JsonValueKind"))
{
    // normalize: treat unhandled kinds as Null or re-materialize the element
    jsValue = JsValue.Null;
}

When it happens

Trigger: Passing a JsonElement whose ValueKind is not one of the handled kinds into TryConvert during JS variable/argument conversion — typically a JsonDocument root element obtained without Read(), or a kind introduced by a newer System.Text.Json version.

Common situations: Passing JsonDocument.RootElement before calling the clone/read pattern; converting values from custom JSON readers; framework upgrades introducing kinds the converter predates; feeding non-standard JSON tokens.

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

• Cannot deserialize to .
• Failed to deserialize
• Invalid variable test values.
• The binding to activity type
• Input ' ' of the ' ' binding does not hold valid JSON

AI-assisted analysis of elsa-workflows/elsa-core@fe9217bdfa (2026-09-13). Data as JSON: /api/errors/90c50377d257110b. Report an issue: GitHub.

Appendix: source

Thrown at src/modules/Elsa.Expressions.JavaScript/ObjectConverters/JsonElementConverter.cs:39

        return false;
    }

    private static JsValue ConvertJsonElementToJsValue(Engine engine, JsonElement element) =>
        element.ValueKind switch
        {
            JsonValueKind.Object => JsValue.FromObject(engine, JsonObject.Create(element)),
            JsonValueKind.Array => JsValue.FromObject(engine, JsonArray.Create(element)),
            // JsString.Create is the counterpart of the JsNumber.Create and JsBoolean uses below: it produces the
            // string value directly, where JsValue.FromObject would re-enter the whole conversion pipeline — the
            // registered object converters, this one included, followed by the default converter's type switch —
            // to arrive at the same call. It became public in Jint 4.15.3.
            JsonValueKind.String => JsString.Create(element.GetString()!),
            JsonValueKind.Number => element.TryGetInt32(out var intValue) ? JsNumber.Create(intValue) : JsNumber.Create(element.GetDouble()),
            JsonValueKind.True => JsBoolean.True,
            JsonValueKind.False => JsBoolean.False,
            JsonValueKind.Undefined => JsValue.Undefined,
            JsonValueKind.Null => JsValue.Null,
            _ => throw new InvalidOperationException($"Unsupported JsonValueKind: {element.ValueKind}")
        };
}

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