JS Practice — Built-in Objects

Object.defineProperties() — non-enumerable property

📖 Usage Example

// Define multiple property descriptors at once
const obj = {}
Object.defineProperties(obj, {
  x: { value: 1, writable: true, enumerable: true },
  y: { value: 2, writable: false, enumerable: true },
})

Use Object.defineProperties() to define multiple properties with fine-grained descriptors in a single call.

Object.defineProperties() — hiding properties

Properties defined with enumerable: false are invisible to Object.keys and for...in.

Challenge: Implement addWithHidden(obj) that adds a visible name property and a hidden _internal property.

const o = {}
addWithHidden(o)
Object.keys(o)           // → ['name']
o._internal              // → 'secret'

💡 Hints (2)

• Set `enumerable: false` on `_internal` to hide it from standard iteration.
• `Object.getOwnPropertyNames` reveals all own properties regardless of enumerability.