```typescript
/** The factorial of n. */
export function factorial(n: number): number {
  /**
   * Throws an Error if n is negative or not an integer.
   */
  if (n < 0) {
    throw new Error("Factorial is not defined for negative numbers");
  }
  
  if (!Number.isInteger(n)) {
    throw new Error("Factorial is only defined for integers");
  }
  
  if (n === 0 || n === 1) {
    return 1;
  }
  return n * factorial(n - 1);
}
```