JS Practice — Built-in Objects

propertyIsEnumerable() — array indices

📖 Usage Example

// Check if a property shows up in for...in loops
const obj = { a: 1 }
obj.propertyIsEnumerable('a')   // → true
Object.defineProperty(obj, 'b', { value: 2, enumerable: false })
obj.propertyIsEnumerable('b')   // → false

Use propertyIsEnumerable() to check whether a specific own property will appear during enumeration (e.g., for...in or Object.keys).

propertyIsEnumerable() — arrays

Array elements at numeric indices are own enumerable properties. propertyIsEnumerable('0') returns true for arrays.

However, the length property of an array is NOT enumerable.

Challenge: Verify array index enumerability.

💡 Hints (1)

• Array indices are strings in property lookup