Reflect.isExtensible()

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.

target

The target object which to check if it is extensible.

A Boolean indicating whether or not the target is extensible.

A TypeError, if target is not an Object.

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().

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

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

• Polyfill of Reflect.isExtensible in core-js
• Reflect
• Object.isExtensible()