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).
Syntax
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
targetis not an object.
- : Thrown if
Description
Reflect.preventExtensions() provides the reflective semantic of preventing extensions of an object. The differences with Object.preventExtensions are:
Reflect.preventExtensions()throws a TypeError if the target is not an object, whileObject.preventExtensions()always returns non-object targets as-is.Reflect.preventExtensions()returns a Boolean indicating whether or not the target was successfully set to prevent extensions, whileObject.preventExtensions()returns the target object.
Reflect.preventExtensions() invokes the <span class="selflink">PreventExtensions</span> object internal method of target.
Examples
Using Reflect.preventExtensions()
See also Object.preventExtensions.
// 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.
Reflect.preventExtensions(1);
// TypeError: 1 is not an object
Object.preventExtensions(1);
// 1