Reflect.isExtensible()

const object1 = {};

console.log(Reflect.isExtensible(object1));
// Expected output: true

Reflect.preventExtensions(object1);

console.log(Reflect.isExtensible(object1));
// Expected output: false

const object2 = Object.seal({});

console.log(Reflect.isExtensible(object2));
// Expected output: false

Reflect.isExtensible(target);

//    
var empty = {};
Reflect.isExtensible(empty); // === true

// ...   
Reflect.preventExtensions(empty);
Reflect.isExtensible(empty); // === false

//    
var sealed = Object.seal({});
Reflect.isExtensible(sealed); // === false

//    
var frozen = Object.freeze({});
Reflect.isExtensible(frozen); // === false

Reflect.isExtensible(1);
// TypeError: 1 is not an object

Object.isExtensible(1);
// false