dotnet/runtime · error · Error

event must be an object, but got

Error message

event must be an object, but got ${JSON.stringify(event)}

What it means

Thrown by `mono_wasm_raise_debug_event` when its first argument is not an object. The function exists to forward structured debugger events to the BrowserDebugProxy via a console.debug magic line, and it requires an object payload to serialise via JSON. Primitives (string/number/boolean/undefined/null) are rejected because the protocol cannot represent them as an event envelope.

Solutions

1. Pass `event` as an object literal that includes `eventName`, e.g. `mono_wasm_raise_debug_event({ eventName: 'X', ... }, args)`.
2. If you have a serialized event, `JSON.parse` it before calling.
3. Add a unit test asserting `typeof event === 'object' && event !== null` at the call site.

Example fix

// before: passed a string
mono_wasm_raise_debug_event('ScriptCompiled', {}); // throws

// after: pass an object
mono_wasm_raise_debug_event({ eventName: 'ScriptCompiled' }, {});

function raiseDebugEventSafe (event, args) {
  if (event === null || typeof event !== 'object') {
    throw new TypeError('event must be a non-null object');
  }
  return mono_wasm_raise_debug_event(event, args);
}

function isDebugEvent (v: unknown): v is object {
  return v !== null && typeof v === 'object';
}

When it happens

Trigger: Calling `mono_wasm_raise_debug_event(event, args)` (debug.ts:130) with `event` being a string, number, boolean, null, or undefined. Usually a caller passed the event name as a string instead of wrapping it in an object, or passed `undefined` by mistake.

Common situations: Custom instrumentation code calling the API with the wrong shape; refactoring that lost the object wrapper; passing a serialized JSON string instead of an object.

Related errors

• args must be an object, but got
• event.eventName is a required parameter, in event
• "arguments" should be an array, but was
• Argument to stringToInternedMonoStringRoot must be a string…
• capacity >= 1

AI-assisted analysis of dotnet/runtime@60108ba66e (2026-08-10). Data as JSON: /api/errors/213466d04d2cc81d. Report an issue: GitHub.

Appendix: source

Thrown at src/mono/browser/runtime/debug.ts:132

    forceThreadMemoryViewRefresh();
}

export function mono_wasm_detach_debugger (): void {
    forceThreadMemoryViewRefresh();
    cwraps.mono_wasm_set_is_debugger_attached(false);
}

export function mono_wasm_change_debugger_log_level (level: number): void {
    forceThreadMemoryViewRefresh();
    cwraps.mono_wasm_change_debugger_log_level(level);
}

/**
 * Raises an event for the debug proxy
 */
export function mono_wasm_raise_debug_event (event: WasmEvent, args = {}): void {
    if (typeof event !== "object")
        throw new Error(`event must be an object, but got ${JSON.stringify(event)}`);

    if (event.eventName === undefined)
        throw new Error(`event.eventName is a required parameter, in event: ${JSON.stringify(event)}`);

    if (typeof args !== "object")
        throw new Error(`args must be an object, but got ${JSON.stringify(args)}`);

    // eslint-disable-next-line no-console
    console.debug("mono_wasm_debug_event_raised:aef14bca-5519-4dfe-b35a-f867abc123ae", JSON.stringify(event), JSON.stringify(args));
}

export function mono_wasm_wait_for_debugger (): Promise<void> {
    return new Promise<void>((resolve) => {
        const interval = setInterval(() => {
            if (runtimeHelpers.waitForDebugger != 1) {
                return;
            }
            clearInterval(interval);

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