dotnet/runtime · error · Error

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

Error message

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

What it means

Thrown by mono_wasm_raise_debug_event() in debug.ts when the `args` parameter (second argument, defaulting to {}) is not of type 'object'. args carries extra event arguments forwarded to the proxy; passing a primitive is a contract violation. The default {} means most callers never hit this; it only fires when a caller explicitly passes a non-object.

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 {

View on GitHub (pinned to 290d5ab72c)

Solutions

1. Omit args (use the default {}) unless you need extra forwarded arguments.
2. If you pass args, pass an object literal: { key: value }.
3. Re-check argument order: (event, args).

Example fix

// before
mono_wasm_raise_debug_event(event, bpId);  // bpId is a number

// after
mono_wasm_raise_debug_event(event, { bpId });
// or simply omit it
mono_wasm_raise_debug_event(event);

function raise(event: WasmEvent, args?: unknown) {
  if (args !== undefined && (args === null || typeof args !== 'object' || Array.isArray(args) === false ? false : true) === false && typeof args !== 'object') {
    throw new TypeError('args must be an object');
  }
  mono_wasm_raise_debug_event(event, (args ?? {}) as any);
}

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

null

When it happens

Trigger: Calling mono_wasm_raise_debug_event(event, 'someString') or (event, 5). A refactor passing a payload value where the args object was expected.

Common situations: Argument-position confusion: passing the payload as the second arg instead of folding it into the event object. Fork code that supplies args positionally.

Related errors

• event must be an object, but got ${JSON.stringify(event)}
• event.eventName is a required parameter, in event: ${JSON.st
• "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/62a2410f8e943cee. Report an issue: GitHub.