dotnet/runtime · error · Error

event.eventName is a required parameter, in event

Error message

event.eventName is a required parameter, in event: ${JSON.stringify(event)}

What it means

Thrown by `mono_wasm_raise_debug_event` when the `event` argument is an object but lacks an `eventName` property. The proxy needs `eventName` to route the event, so its absence makes the event unprocessable.

Solutions

1. Always set `eventName` explicitly on the event object literal.
2. If building the event programmatically, assert the key is set before calling (`if (!event.eventName) return;`).
3. Use a typed factory function whose return type requires `eventName`.

Example fix

// before: object without eventName
mono_wasm_raise_debug_event({ threadId: 1 }, {}); // throws

// after: include eventName
mono_wasm_raise_debug_event({ eventName: 'ThreadStarted', threadId: 1 }, {});

function raiseDebugEventSafe (event, args) {
  if (!event || typeof event !== 'object' || event.eventName === undefined) {
    throw new TypeError('event.eventName is required');
  }
  return mono_wasm_raise_debug_event(event, args);
}

function hasEventName (v: unknown): v is { eventName: string } {
  return v !== null && typeof v === 'object' && typeof (v as any).eventName === 'string';
}

When it happens

Trigger: Calling `mono_wasm_raise_debug_event(event, args)` (debug.ts:134) where `event` is `{}` or has properties but no `eventName`. Typical when constructing the event dynamically and forgetting to set `eventName`, or when spreading defaults that overwrite it to undefined.

Common situations: Refactoring an event builder that dropped the `eventName` field; computing the field conditionally and leaving it unset; copy-paste from an event schema that renamed the field.

Related errors

• args must be an object, but got
• event must be an object, but got
• "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/e9a2a90f5b725b11. Report an issue: GitHub.

Appendix: source

Thrown at src/mono/browser/runtime/debug.ts:135

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);
            resolve();
        }, 100);
    });

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