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:

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 Latest Draft (ECMA-262)
The definition of '[[IsExtensible]]' in that specification.
Draft  

Browser compatibility

Update compatibility data on GitHub
DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
isExtensibleChrome Full support 49Edge Full support 12Firefox Full support 31IE No support NoOpera Full support 36Safari ? WebView Android Full support 49Chrome Android Full support 49Firefox Android Full support 31Opera Android Full support 36Safari iOS ? Samsung Internet Android Full support 5.0nodejs Full support 6.0.0

Legend

Full support  
Full support
No support  
No support
Compatibility unknown  
Compatibility unknown

See also