Reflect.isExtensible()
Baseline Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since September 2016.
The Reflect.isExtensible()
static method is like Object.isExtensible()
. It determines if an object is extensible (whether it can have new properties added to it).
Try it
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
target
is not an object.
Description
Reflect.isExtensible()
provides the reflective semantic of checking if an object is extensible. The only difference with Object.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 Object.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 Object.isExtensible()
, a non-object target
will return false without any errors.
Reflect.isExtensible(1);
// TypeError: 1 is not an object
Object.isExtensible(1);
// false
Specifications
Specification |
---|
ECMAScript Language Specification # sec-reflect.isextensible |
Browser compatibility
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