javascript static method
Reflect.preventExtensions()
The Reflect.preventExtensions() static method is like preventExtensions(). It prevents new properties from ever being added to an object (i.e., prevents future extensions to the object).
const object = {};
console.log(Reflect.isExtensible(object));
// Expected output: true
Reflect.preventExtensions(object);
console.log(Reflect.isExtensible(object));
// Expected output: false
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 preventExtensions() are:
Reflect.preventExtensions()throws aTypeErrorif the target is not an object, whileObject.preventExtensions()always returns non-object targets as-is.Reflect.preventExtensions()returns aBooleanindicating 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 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 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