JS Practice — Built-in Objects

Proxy has trap — only x is present

📖 Usage Example

const p = new Proxy({}, {
  has: (target, key) => key.startsWith('a')
})
console.log('apple' in p)  // → true
console.log('banana' in p) // → false

The has trap intercepts the in operator, allowing you to control which property names are considered present on a proxy.

has trap — selective key visibility

The has trap receives (target, key). You can conditionally return true only for specific keys.

Challenge: Verify that 'x' in p is true when has returns key === 'x'.

💡 Hints (1)