JS Practice — Built-in Objects

Type Guard — isPositiveNumber

📖 Usage Example

function isPositiveNumber(x: unknown): x is number {
  return typeof x === 'number' && x > 0
}
isPositiveNumber(5)    // → true
isPositiveNumber(-1)   // → false

Combining a typeof check with a value constraint creates a refined numeric type guard.

Type Guards: Combined Conditions

Challenge: Implement isPositiveNumber(x: unknown): x is number — true only if x is a finite, positive number (not NaN, not Infinity, not zero).

isPositiveNumber(5)        // → true
isPositiveNumber(-1)       // → false
isPositiveNumber(0)        // → false
isPositiveNumber(Infinity) // → false

💡 Hints (1)

• typeof check + Number.isFinite + x > 0.