dotnet/runtime · error · Error

event.eventName is a required parameter, in event: ${JSON.st

Error message

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

What it means

Thrown by mono_wasm_raise_debug_event() in debug.ts when `event` is an object but lacks the required `eventName` property. The BrowserDebugProxy routes events by eventName, so an anonymous event object cannot be dispatched. This is the event-contract validation that runs right after the object-type check.

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);
    });

View on GitHub (pinned to 290d5ab72c)

Solutions

1. Always set event.eventName to a known event string before raising.
2. Double-check the key spelling/case: it must be exactly `eventName`.
3. Type the event as WasmEvent ({ eventName: string, [k: string]: any }) so the compiler catches a missing field.

Example fix

// before
mono_wasm_raise_debug_event({ id: 1 });  // throws: no eventName

// after
mono_wasm_raise_debug_event({ eventName: 'scriptLoaded', id: 1 });

function raiseEvent(event: { eventName?: string }) {
  if (!event || typeof event.eventName !== 'string' || !event.eventName) {
    throw new Error('eventName is required and must be a non-empty string');
  }
  mono_wasm_raise_debug_event(event as WasmEvent);
}

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

null

When it happens

Trigger: Calling mono_wasm_raise_debug_event({ payload }) with no eventName field, or with eventName misspelled (e.g. EventName, event_name). A builder that spreads payload fields but forgets to set eventName.

Common situations: Refactoring event construction and dropping the eventName key. Case mismatch on the key (eventName is case-sensitive). Passing a details object where the caller expected the full event.

Related errors

• event must be an object, but got ${JSON.stringify(event)}
• args must be an object, but got ${JSON.stringify(args)}
• "arguments" should be an array, but was ${request.arguments}
• Failed on mono_wasm_send_dbg_command_with_parms
• Failed on mono_wasm_send_dbg_command

AI-assisted analysis of dotnet/runtime@290d5ab72c (2026-08-06). Data as JSON: /api/errors/e9a2a90f5b725b11. Report an issue: GitHub.