preventExtensions()

The Reflect.preventExtensions method is employed to prohibit any further extensions to an object. It serves the same purpose as the Object.preventExtensions method.

Syntax:

Reflect.preventExtensions(obj)

Parameters:

Subject: This is the target entity for which extensions are to be restricted.

Return value:

The function will return a boolean value of true if the target has been effectively set to block extensions. If not successful, the function will return false.

Exceptions:

A TypeError, if the target is not an Object.

Browser Support:

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:

false
false