Web/JavaScript/Reference/Global objects/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.

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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

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.

Update compatibility data on GitHub

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
preventExtensions	Chrome Full support 49	Edge Full support 12	Firefox Full support 42	IE No support No	Opera Full support 36	Safari Full support 10	WebView Android Full support 49	Chrome Android Full support 49	Firefox Android Full support 42	Opera Android Full support 36	Safari iOS Full support 10	Samsung Internet Android Full support 5.0	nodejs Full support 6.0.0

Legend

Full support  

Full support

No support  

No support

See also

• Reflect
• Object.isExtensible()

Reflect.preventExtensions() by Mozilla Contributors is licensed under CC-BY-SA 2.5.