Proxy.handler.isExtensible

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

Syntax

var p = new Proxy(target, {
  isExtensible: function(target) {
  }
});

Parameters

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

target

The target object.

Return value

The isExtensible method must return a boolean value.

Description

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

Interceptions

This trap can intercept these operations:

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

Invariants

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

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

Examples

The following code traps Object.isExtensible().

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

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

The following code violates the invariant.

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

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

Specifications

Specification	Status	Comment
ECMAScript 2015 (6th Edition, ECMA-262) The definition of '[[IsExtensible]]' in that specification.	Standard	Initial definition.
ECMAScript 2017 Draft (ECMA-262) The definition of '[[IsExtensible]]' in that specification.	Draft

Browser compatibility

See also

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