dotnet/aspnetcore · error · Error

Supplied value is not a typed array or blob.

Error message

Supplied value is not a typed array or blob.

What it means

Thrown by DotNet.createJSStreamReference() when the supplied value is neither a Blob nor has a .buffer property that is an ArrayBuffer. The stream reference path only supports Blob or ArrayBufferView inputs; anything else is rejected before length is computed.

Solutions

1. Convert the data to a Blob: createJSStreamReference(new Blob([data])).
2. Convert to a Uint8Array: createJSStreamReference(new Uint8Array(data)).
3. For raw ArrayBuffer, it is auto-wrapped to Uint8Array by the function — pass it directly.

Example fix

// before
const ref = createJSStreamReference(readableStream); // ReadableStream is not Blob/TypedArray

// after
const blob = await new Response(readableStream).blob();
const ref = createJSStreamReference(blob);

function isStreamable(v) { return v instanceof Blob || (v != null && v.buffer instanceof ArrayBuffer); }
if (!isStreamable(value)) { value = new Blob([value]); } // normalize
const ref = DotNet.createJSStreamReference(value);

function isStreamInput(v: unknown): v is Blob | ArrayBufferView { return v instanceof Blob || (v != null && (v as any).buffer instanceof ArrayBuffer); }

try { return DotNet.createJSStreamReference(value); } catch (e) { throw new Error('createJSStreamReference requires a Blob, ArrayBuffer, or typed array.', { cause: e }); }

When it happens

Trigger: Passing a plain object, a string, a number, a ReadableStream, or any value that is not instanceof Blob and whose .buffer is not an ArrayBuffer. E.g., createJSStreamReference({ data: [1,2,3] }).

Common situations: Trying to stream a ReadableStream directly instead of a Blob/typed array; passing fetch Response body objects; misunderstanding the API as a generic stream sender.

Related errors

• Cannot create a JSStreamReference from the value
• Cannot create a JSStreamReference from the value
• Byte array index ' ' does not exist.
• Cannot create a JSObjectReference from the value
• Invalid JS call result type

AI-assisted analysis of dotnet/aspnetcore@3600ca084e (2026-08-11). Data as JSON: /api/errors/a162b0a236920ce6. Report an issue: GitHub.

Appendix: source

Thrown at src/JSInterop/Microsoft.JSInterop.JS/src/src/Microsoft.JSInterop.ts:208

  export function createJSStreamReference(streamReference: ArrayBuffer | ArrayBufferView | Blob | any): any {
      let length = -1;

      // If we're given a raw Array Buffer, we interpret it as a `Uint8Array` as
      // ArrayBuffers' aren't directly readable.
      if (streamReference instanceof ArrayBuffer) {
          streamReference = new Uint8Array(streamReference);
      }

      if (streamReference instanceof Blob) {
          length = streamReference.size;
      } else if (streamReference.buffer instanceof ArrayBuffer) {
          if (streamReference.byteLength === undefined) {
              throw new Error(`Cannot create a JSStreamReference from the value '${streamReference}' as it doesn't have a byteLength.`);
          }

          length = streamReference.byteLength;
      } else {
          throw new Error("Supplied value is not a typed array or blob.");
      }

      const result: any = {
          [jsStreamReferenceLengthKey]: length
      };

      try {
          const jsObjectReference = createJSObjectReference(streamReference);
          result[jsObjectIdKey] = jsObjectReference[jsObjectIdKey];
      } catch (error) {
          throw new Error(`Cannot create a JSStreamReference from the value '${streamReference}'.`);
      }

      return result;
  }

  /**
   * Disposes the given JavaScript object reference.

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