JavaScript Reflect.preventExtensions() Method

The static Reflect.preventExtensions() method is used prevent future extensions to the object. This method is same as Object.preventExtensions() method.

Syntax:

Parameters:

Obj: It is the object on which to prevent extensions.

Return value:

This method returns true if the target was successfully set to prevent extensions. Otherwise, this method returns false.

Exceptions:

A TypeError, if the target is not an Object.

Browser Support:

Chrome	49
Edge	12
Firefox	42
Opera	36

Example 1

const u = {};
console.log ( Reflect.isExtensible ( u ) ); 
Reflect.preventExtensions ( u );
console.log ( Reflect.isExtensible ( u ) ); 

Output:

true
false

Example 2

const obj = {"p":3,"q":4};
Reflect.preventExtensions(obj);
console.log ( obj.hasOwnProperty ( "p" ) ); 
delete obj.p;
console.log ( obj.hasOwnProperty ( "q" ) );

Output:

true
true

Example 3

const uu = {};
Reflect.preventExtensions(uu);
console.log(
Reflect.isExtensible(uu)
); 
// add a property
uu.pp = 3;
console.log(
    uu.hasOwnProperty ("pp")
);

Output: