Reflect.preventExtensions() - JavaScript 编辑

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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The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

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

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See also

• Reflect
• Object.isExtensible()