dotnet/runtime · error · Error

args must be an object, but got

Error message

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

What it means

Thrown by `mono_wasm_raise_debug_event` when the optional `args` argument is present but not an object. The default `{}` is fine; passing a primitive (e.g. an array or string) violates the contract that args is a key/value bag serialised as JSON alongside the event.

Solutions

1. Omit `args` (or pass `{}`) when there are no extra parameters.
2. If you have positional data, wrap it: `{ params: [...] }`.
3. Ensure helper builders return `{}` rather than `null` for the no-args case.

Example fix

// before: array passed as args
mono_wasm_raise_debug_event(ev, ['a', 'b']); // throws

// after: wrap positional data in an object
mono_wasm_raise_debug_event(ev, { params: ['a', 'b'] });

function raiseDebugEventSafe (event, args) {
  const safeArgs = args === undefined ? {} : args;
  if (safeArgs === null || typeof safeArgs !== 'object') {
    throw new TypeError('args must be an object');
  }
  return mono_wasm_raise_debug_event(event, safeArgs);
}

function isArgsBag (v: unknown): v is Record<string, unknown> {
  return v !== null && typeof v === 'object' && !Array.isArray(v);
}

When it happens

Trigger: Calling `mono_wasm_raise_debug_event(event, args)` (debug.ts:137) where `args` is a string, number, array, null, or boolean. Most commonly the caller passes a positional array of values, or passes `null` thinking it means 'no args'.

Common situations: Refactoring that changed args from object to array; passing the result of a function that returns null on empty; misunderstanding that `null` is not an object (typeof null === 'object' is true, but here null still triggers because the runtime asserts the value before that quirk only when args !== undefined — note the check is `typeof args !== 'object'`, which lets null through, so the realistic trigger is arrays/strings/numbers/booleans).

Related errors

• event.eventName is a required parameter, in event
• 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/62a2410f8e943cee. Report an issue: GitHub.

Appendix: source

Thrown at src/mono/browser/runtime/debug.ts:138

}

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);
    });
}

export function mono_wasm_debugger_attached (): void {

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