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Proxy.proxy.isExtensible

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

Syntax

const 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

Trapping of isExtensible

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

Specifications

Browser compatibilityUpdate compatibility data on GitHub

Desktop
Chrome Edge Firefox Internet Explorer Opera Safari
isExtensible 49 12 31 No 36 10
Mobile
Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet
isExtensible 49 49 31 36 10 5.0
Server
Node.js
isExtensible 6.0.0

See also

© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://wiki.developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy/Proxy/isExtensible