Reflect.preventExtensions()

The static Reflect.preventExtensions() method prevents new properties from ever being added to an object (i.e., prevents future extensions to the object). It is similar to Object.preventExtensions(), but with some differences.

Syntax

Reflect.preventExtensions(target)

Parameters

target
The target object on which to prevent extensions.

Return value

A Boolean indicating whether or not the target was successfully set to prevent extensions.

Exceptions

A TypeError, if target is not an Object.

Description

The Reflect.preventExtensions() method allows you to prevent new properties from ever being added to an object (i.e., prevents future extensions to the object). It is similar to Object.preventExtensions().

Examples

Using Reflect.preventExtensions()

See also Object.preventExtensions().

// Objects are extensible by default.
let empty = {}
Reflect.isExtensible(empty)  // === true

// ...but that can be changed.
Reflect.preventExtensions(empty)
Reflect.isExtensible(empty)  // === false

Difference from Object.preventExtensions()

If the target argument to this method is not an object (a primitive), then it will cause a TypeError. With Object.preventExtensions(), a non-object target will be coerced to an object.

Reflect.preventExtensions(1)
// TypeError: 1 is not an object

Object.preventExtensions(1)
// 1

Specifications

Specification
ECMAScript (ECMA-262)
The definition of 'Reflect.preventExtensions' in that specification.

Browser compatibility

DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
preventExtensionsChrome Full support 49Edge Full support 12Firefox Full support 42IE No support NoOpera Full support 36Safari Full support 10WebView Android Full support 49Chrome Android Full support 49Firefox Android Full support 42Opera Android Full support 36Safari iOS Full support 10Samsung Internet Android Full support 5.0nodejs Full support 6.0.0

Legend

Full support
Full support
No support
No support

See also