denoland/deno · error · TypeError

Unexpected 'fn' field in options, bench function is already

Error message

Unexpected 'fn' field in options, bench function is already provided as the second argument

What it means

The desktop icon file exists but its extension is neither `.icns` nor `.png` — the only formats accepted by the laufey `NSImage initWithContentsOfFile:` path used here, so no conversion is attempted and startup aborts.

Source

Thrown at cli/js/40_bench.js:162

    }
    if (optionsOrFn != undefined) {
      throw new TypeError("Unexpected second argument to Deno.bench()");
    }
    if (maybeFn != undefined) {
      throw new TypeError("Unexpected third argument to Deno.bench()");
    }
    benchDesc = {
      ...defaults,
      fn: nameOrFnOrOptions,
      name: nameOrFnOrOptions.name,
    };
  } else {
    let fn;
    let name;
    if (typeof optionsOrFn === "function") {
      fn = optionsOrFn;
      if (nameOrFnOrOptions.fn != undefined) {
        throw new TypeError(
          "Unexpected 'fn' field in options, bench function is already provided as the second argument",
        );
      }
      name = nameOrFnOrOptions.name ?? fn.name;
    } else {
      if (
        !nameOrFnOrOptions.fn || typeof nameOrFnOrOptions.fn !== "function"
      ) {
        throw new TypeError(
          "Expected 'fn' field in the first argument to be a bench function",
        );
      }
      fn = nameOrFnOrOptions.fn;
      name = nameOrFnOrOptions.name ?? fn.name;
    }
    if (!name) {
      throw new TypeError("The bench name can't be empty");
    }

View on GitHub (pinned to 89f33cbef2)

Solutions

1. Convert the image to PNG, e.g. `magick assets/logo.svg assets/logo.png`
2. Or convert to `.icns` if you want the macOS native format
3. Point the `icon` config at the converted `.png`/`.icns` file

Example fix

// before
"icon": "assets/logo.svg"

// after
// $ magick assets/logo.svg assets/logo.png
"icon": "assets/logo.png"

const ext = iconPath.split('.').pop()?.toLowerCase();
if (ext !== 'png' && ext !== 'icns') {
  throw new Error(`icon must be .png or .icns, got .${ext}`);
}

function isSupportedIcon(p: string): boolean {
  return /\.(png|icns)$/i.test(p);
}

When it happens

Trigger: Passing `.jpg`, `.jpeg`, `.svg`, `.ico`, `.webp`, or an extensionless file as the desktop icon on macOS.

Common situations: Reusing a web favicon (.ico/.svg), marketing photo (.jpg), or design-tool export (.webp) as the app icon.

Related errors

• Unexpected second argument to Deno.bench()
• Unexpected 'name' field in options, bench name is already pr
• Unexpected third argument to Deno.bench()
• Either `node` or `range` must be provided when reporting an
• Invalid range. Start value is bigger than end value: [${star

AI-assisted analysis of denoland/deno@89f33cbef2 (2026-08-16). Data as JSON: /api/errors/53d16d74784e79a0. Report an issue: GitHub.