JS Practice — Built-in Objects

Proxy has trap — passthrough for existing key

📖 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 — passthrough

Without a has trap, the in operator checks the target directly.

Challenge: Verify that 'a' in new Proxy({a: 1}, {}) is true.

💡 Hints (1)