handler.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 compatibility

Desktop Mobile
Chrome Edge Firefox Internet Explorer Opera Safari WebView Android Chrome Android Firefox for Android Opera Android Safari on IOS Samsung Internet
isExtensible
49
12
31
No
36
10
49
49
31
36
10
5.0

See also

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Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy/Proxy/isExtensible