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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

Browser compatibilityUpdate compatibility data on GitHub

Desktop
Chrome Edge Firefox Internet Explorer Opera Safari
preventExtensions 49 12 42 No 36 10
Mobile
Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet
preventExtensions 49 49 42 36 10 5.0
Server
Node.js
preventExtensions 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/Reflect/preventExtensions