代码翻译

export function add(a: number, b: number): number { return a + b; }

Notes:

• The TypeScript version explicitly accepts and returns number.
• Unlike the JavaScript original, calls with strings or other non-number values are rejected at compile time.
• TypeScript types are erased at runtime, so JavaScript callers can still pass incompatible values unless runtime validation is added.
• number includes floating-point values, NaN, and Infinity.
• JavaScript’s usual numeric behavior still applies, including floating-point precision issues and coercion at runtime.