javascript static method
Reflect.isExtensible()
The Reflect.isExtensible() static method is like isExtensible(). It determines if an object is extensible (whether it can have new properties added to it).
const object1 = {};
console.log(Reflect.isExtensible(object1));
// Expected output: true
Reflect.preventExtensions(object1);
console.log(Reflect.isExtensible(object1));
// Expected output: false
const object2 = Object.seal({});
console.log(Reflect.isExtensible(object2));
// Expected output: false
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
TypeError- : Thrown if
targetis not an object.
- : Thrown if
Description
Reflect.isExtensible() provides the reflective semantic of checking if an object is extensible. The only difference with isExtensible() is how non-object targets are handled. Reflect.isExtensible() throws a TypeError if the target is not an object, while Object.isExtensible() always returns false for non-object targets.
Reflect.isExtensible() invokes the [[IsExtensible]] object internal method of target.
Examples
Using Reflect.isExtensible()
See also isExtensible().
// New objects are extensible.
const empty = {};
Reflect.isExtensible(empty); // true
// … but that can be changed.
Reflect.preventExtensions(empty);
Reflect.isExtensible(empty); // false
// Sealed objects are by definition non-extensible.
const sealed = Object.seal({});
Reflect.isExtensible(sealed); // false
// Frozen objects are also by definition non-extensible.
const frozen = Object.freeze({});
Reflect.isExtensible(frozen); // false
Difference with Object.isExtensible()
If the target argument to this method is not an object (a primitive), then it will cause a TypeError. With isExtensible(), a non-object target will return false without any errors.
Reflect.isExtensible(1);
// TypeError: 1 is not an object
Object.isExtensible(1);
// false