Reflect.isExtensible() - JavaScript 编辑

The static Reflect.isExtensible() method determines if an object is extensible (whether it can have new properties added to it). It is similar to Object.isExtensible(), but with some differences.

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.

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.isExtensible(target)

Parameters

target

The target object which to check if it is extensible.

Return value

A Boolean indicating whether or not the target is extensible.

Exceptions

A TypeError, if target is not an Object.

Description

The Reflect.isExtensible method allows you determine if an object is extensible (whether it can have new properties added to it). It is the same method as Object.isExtensible().

Examples

Using Reflect.isExtensible()

See also Object.isExtensible().

// New objects are extensible.
let empty = {}
Reflect.isExtensible(empty)  // === true

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

// Sealed objects are by definition non-extensible.
let sealed = Object.seal({})
Reflect.isExtensible(sealed)  // === false

// Frozen objects are also by definition non-extensible.
let frozen = Object.freeze({})
Reflect.isExtensible(frozen)  // === false

Difference to Object.isExtensible()

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

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

Object.isExtensible(1)
// false

Specifications

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

Browser compatibility

BCD tables only load in the browser

See also

• Reflect
• Object.isExtensible()