The handler.preventExtensions()
method is a trap for Object.preventExtensions()
.
Syntax
var p = new Proxy(target, { preventExtensions: function(target) { } });
Parameters
The following parameter is passed to the preventExtensions
method. this
is bound to the handler.
target
- The target object.
Return value
The preventExtensions
method must return a boolean value.
Description
The handler.preventExtensions()
method is a trap for Object.preventExtensions()
.
Interceptions
This trap can intercept these operations:
Invariants
If the following invariants are violated, the proxy will throw a TypeError
:
Object.preventExtensions(proxy)
only returnstrue
ifObject.isExtensible(proxy)
isfalse
.
Examples
The following code traps Object.preventExtensions()
.
var p = new Proxy({}, { preventExtensions: function(target) { console.log('called'); Object.preventExtensions(target); return true; } }); console.log(Object.preventExtensions(p)); // "called" // false
The following code violates the invariant.
var p = new Proxy({}, { preventExtensions: function(target) { return true; } }); Object.preventExtensions(p); // TypeError is thrown
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript 2015 (6th Edition, ECMA-262) The definition of '[[PreventExtensions]]' in that specification. |
Standard | Initial definition. |
ECMAScript Latest Draft (ECMA-262) The definition of '[[PreventExtensions]]' in that specification. |
Living Standard |
Browser compatibility
The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.
Feature | Chrome | Edge | Firefox | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|---|
Basic support | 49 | 12 | 22 | No | 36 | 10 |
Feature | Android webview | Chrome for Android | Edge mobile | Firefox for Android | IE mobile | Opera Android | iOS Safari |
---|---|---|---|---|---|---|---|
Basic support | 49 | 49 | Yes | 22 | No | 36 | 10 |