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 the same method as Object.preventExtensions().

Examples

Using Reflect.preventExtensions()

See also Object.preventExtensions().

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

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

Difference to Object.preventExtensions()

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

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

Object.preventExtensions(1);
// 1

Specifications

Specification	Status	Comment
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Reflect.preventExtensions' in that specification.	Standard	Initial definition.
ECMAScript 2017 Draft (ECMA-262) The definition of 'Reflect.preventExtensions' in that specification.	Draft

Browser compatibility

See also

• Reflect
• Object.isExtensible()