dotnet/runtime · error · Error

NotImplementedException: TypedArray

Error message

NotImplementedException: TypedArray

What it means

marshal_cs_object_to_cs supports only Uint8Array, Float32Array, Float64Array, Int32Array and plain Array as array-like objects. Other TypedArray variants (Int8Array, Int16Array, Uint8ClampedArray, Uint16Array, Uint32Array) hit the else-branch and throw NotImplementedException: TypedArray.

Source

Thrown at src/mono/browser/runtime/marshal-to-cs.ts:417

            } else if (value instanceof Error) {
                marshal_exception_to_cs(arg, value);
            } else if (value instanceof Uint8Array) {
                marshal_array_to_cs_impl(arg, value, MarshalerType.Byte);
            } else if (value instanceof Float32Array) {
                marshal_array_to_cs_impl(arg, value, MarshalerType.Single);
            } else if (value instanceof Float64Array) {
                marshal_array_to_cs_impl(arg, value, MarshalerType.Double);
            } else if (value instanceof Int32Array) {
                marshal_array_to_cs_impl(arg, value, MarshalerType.Int32);
            } else if (Array.isArray(value)) {
                marshal_array_to_cs_impl(arg, value, MarshalerType.Object);
            } else if (value instanceof Int16Array
                || value instanceof Int8Array
                || value instanceof Uint8ClampedArray
                || value instanceof Uint16Array
                || value instanceof Uint32Array
            ) {
                throw new Error("NotImplementedException: TypedArray");
            } else if (isThenable(value)) {
                marshal_task_to_cs(arg, value);
            } else if (value instanceof Span) {
                throw new Error("NotImplementedException: Span");
            } else if (js_type == "object") {
                const js_handle = mono_wasm_get_js_handle(value);
                set_arg_type(arg, MarshalerType.JSObject);
                if (BuildConfiguration === "Debug" && Object.isExtensible(value)) {
                    value[proxy_debug_symbol] = `JS Object with JSHandle ${js_handle}`;
                }
                set_js_handle(arg, js_handle);
            } else {
                throw new Error(`JSObject proxy is not supported for ${js_type} ${value}`);
            }
        } else {
            assert_not_disposed(value);
            if (value instanceof ArraySegment) {
                throw new Error("NotImplementedException: ArraySegment. " + jsinteropDoc);

View on GitHub (pinned to 290d5ab72c)

Solutions

1. Convert the array to one of the supported views: Uint8Array, Int32Array, Float32Array, Float64Array, or a plain Array.
2. If the C# parameter should be a typed buffer, declare it as byte[]/int[]/float[]/double[] so the matching array marshaler is selected.

Example fix

// before
dotnet.jsExports.Take(new Uint16Array([1,2,3])); // throws
// after
dotnet.jsExports.Take(new Uint8Array([1,2,3]));
// or declare C# param as ushort[] via a supported element type

const UNSUPPORTED = new Set([Int8Array, Int16Array, Uint16Array, Uint32Array, Uint8ClampedArray]);
for (const T of UNSUPPORTED) if (value instanceof T) throw new TypeError(`${T.name} is not supported by the object marshaler; use Uint8Array/Int32Array/Float32Array/Float64Array/Array.`);

function isSupportedTypedArray(v: unknown): v is Uint8Array | Int32Array | Float32Array | Float64Array { return v instanceof Uint8Array || v instanceof Int32Array || v instanceof Float32Array || v instanceof Float64Array; }

When it happens

Trigger: Passing an Int8Array, Uint16Array, Int16Array, Uint8ClampedArray, or Uint32Array to a C# [JSExport] parameter typed as object/JSObject.

Common situations: Using a Uint16Array or Int16Array for audio/graphics data; picking a TypedArray width that is not in the supported set when calling loosely-typed interop.

Related errors

• NotImplementedException: bigint
• JSObject proxy is not supported for ${js_type} ${value}
• NotImplementedException ${element_type}
• NotImplementedException: TypedArray
• ${function_name} must be a Function but was ${typeof fn}

AI-assisted analysis of dotnet/runtime@290d5ab72c (2026-08-06). Data as JSON: /api/errors/a2e6a9a3c2c090ab. Report an issue: GitHub.