Object.isFrozen()

gistfile1.js

var obj13 = Object.create({});
obj13.foo = 'x';
obj13.bar = 'y';

Object.freeze( obj13 ); // freezes the object completely

Object.isFrozen( obj13 ); // returns true

Object.isFrozen({}); // returns false because a newly created object is extensible by default

var frozenObj = Object.preventExtensions({});
Object.isFrozen( frozenObj ); // returns true since we have set it to be non-extensible

var obj14 = { x : true };
Object.isFrozen( obj14 ); // returns false because new objects with properties are extensible

Object.preventExtensions( obj14 ); // returns false because the object is still configurable and writable
delete obj14.x;
Object.isFrozen( obj14 ); // returns true as an object with no properties that is not newly created becomes frozen