dotnet/aspnetcore · error · Error

JS object instance with Id

Error message

JS object instance with Id '${id}' does not exist. It may have been disposed.

What it means

Thrown by the built-in reviveReference JSON reviver when deserializing a payload that carries a __jsObjectId marker whose ID is not in cachedJSObjectsById. This fires during JSON.parse of arguments coming from .NET; the .NET side referenced a JS object that the JS runtime no longer holds (disposed or never existed on this client). Distinct from error 91 (which fires at call dispatch time); this fires during argument deserialization.

Solutions

1. Do not send disposed JS object references back from .NET; track disposal on the .NET side.
2. After a reconnect, re-establish JS references rather than reusing stale IDs.
3. Avoid persisting/serializing IJSObjectReference IDs across sessions.

Example fix

// C# before
var jsRef = await JS.InvokeAsync<IJSObjectReference>("getRef");
await jsRef.DisposeAsync();
await JS.InvokeVoidAsync("useRef", jsRef); // sends disposed id -> reviver throws

// after
await jsRef.DisposeAsync();
jsRef = null;
// re-acquire before passing back

// .NET: do not pass disposed IJSObjectReference back to JS.
if (jsRef is null || _disposed) { return; }
await JS.InvokeVoidAsync("useRef", jsRef);

try { /* call that round-trips a jsRef */ } catch (JSException e) when (e.Message.Contains("does not exist. It may have been disposed")) { jsRef = null; /* re-acquire or stop using */ }

When it happens

Trigger: .NET sends back a JS object reference (e.g. round-tripping an IJSObjectReference) that was disposed on the JS side, or whose ID belongs to a different Blazor circuit/session. The reviver cannot resolve the marker to a wrapped object.

Common situations: Round-tripping a disposed IJSObjectReference; Blazor Server circuit reconnect where the JS-side object cache was reset but .NET still holds old IDs; cross-frame/cross-window references.

Related errors

• Byte array index ' ' does not exist.
• Cannot create a JSObjectReference from the value
• Cannot create a JSStreamReference from the value
• JS object instance with ID
• Cannot create a JSStreamReference from the value

AI-assisted analysis of dotnet/aspnetcore@3600ca084e (2026-08-11). Data as JSON: /api/errors/84e2e8cceda2f63f. Report an issue: GitHub.

Appendix: source

Thrown at src/JSInterop/Microsoft.JSInterop.JS/src/src/Microsoft.JSInterop.ts:739

      public serializeAsArg() {
          return { [dotNetObjectRefKey]: this._id };
      }
  }

  attachReviver(function reviveReference(key: any, value: any) {
      if (value && typeof value === "object") {
          if (value.hasOwnProperty(dotNetObjectRefKey)) {
              return new DotNetObject(value[dotNetObjectRefKey], currentCallDispatcher!);
          } else if (value.hasOwnProperty(jsObjectIdKey)) {
              const id = value[jsObjectIdKey];
              const jsObject = cachedJSObjectsById[id];

              if (jsObject) {
                  return jsObject.getWrappedObject();
              }

              throw new Error(`JS object instance with Id '${id}' does not exist. It may have been disposed.`);
          } else if (value.hasOwnProperty(byteArrayRefKey)) {
              const index = value[byteArrayRefKey];
              const byteArray = currentCallDispatcher!.processByteArray(index);
              if (byteArray === undefined) {
                  throw new Error(`Byte array index '${index}' does not exist.`);
              }
              return byteArray;
          } else if (value.hasOwnProperty(dotNetStreamRefKey)) {
              const streamId = value[dotNetStreamRefKey];
              const streamPromise = currentCallDispatcher!.getDotNetStreamPromise(streamId);
              return new DotNetStream(streamPromise);
          }
      }

      // Unrecognized - let another reviver handle it
      return value;
  });

View on GitHub (pinned to 3600ca084e)