Reflect.preventExtensions()
The Reflect.preventExtensions()
static method is like Object.preventExtensions()
. It prevents new properties from ever being added to an object (i.e., prevents future extensions to the object).
Try it
Syntax
js
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
TypeError
-
Thrown if
target
is not an object.
Description
Reflect.preventExtensions()
provides the reflective semantic of preventing extensions of an object. The differences with Object.preventExtensions()
are:
Reflect.preventExtensions()
throws aTypeError
if the target is not an object, whileObject.preventExtensions()
always returns non-object targets as-is.Reflect.preventExtensions()
returns aBoolean
indicating whether or not the target was successfully set to prevent extensions, whileObject.preventExtensions()
returns the target object.
Reflect.preventExtensions()
invokes the [[PreventExtensions]]
object internal method of target
.
Examples
Using Reflect.preventExtensions()
See also Object.preventExtensions()
.
js
// Objects are extensible by default.
const empty = {};
Reflect.isExtensible(empty); // true
// ...but that can be changed.
Reflect.preventExtensions(empty);
Reflect.isExtensible(empty); // false
Difference with 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 returned as-is without any errors.
js
Reflect.preventExtensions(1);
// TypeError: 1 is not an object
Object.preventExtensions(1);
// 1
Specifications
Specification |
---|
ECMAScript Language Specification # sec-reflect.preventextensions |
Browser compatibility
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