handler.isExtensible()

The following parameter is passed to the isExtensible() method. this is bound to the handler.

target

The target object.

The isExtensible() method must return a boolean value.

The handler.isExtensible() method is a trap for Object.isExtensible().

This trap can intercept these operations:

• Object.isExtensible()
• Reflect.isExtensible()

If the following invariants are violated, the proxy will throw a TypeError:

• Object.isExtensible(proxy) must return the same value as Object.isExtensible(target).

The following code traps Object.isExtensible().

const p = new Proxy({}, {
  isExtensible: function(target) {
    console.log('called');
    return true;
  }
});

console.log(Object.isExtensible(p)); // "called"
                                     // true

The following code violates the invariant.

const p = new Proxy({}, {
  isExtensible: function(target) {
    return false;
  }
});

Object.isExtensible(p); // TypeError is thrown

• Proxy
• handler
• Object.isExtensible()
• Reflect.isExtensible()
• Reflect.preventExtensions()