Object.seal()

const object1 = {
  property1: 42,
};

Object.seal(object1);
object1.property1 = 33;
console.log(object1.property1);
// Expected output: 33

delete object1.property1; // Cannot delete when sealed
console.log(object1.property1);
// Expected output: 33

Object.seal(obj);

var obj = {
  prop: function () {},
  foo: "bar",
};

//   ,      
obj.foo = "baz";
obj.lumpy = "woof";
delete obj.prop;

var o = Object.seal(obj);

assert(o === obj);
assert(Object.isSealed(obj) === true);

//         
obj.foo = "quux";
obj.foo; // 'quux'  

//       
Object.defineProperty(obj, "foo", {
  get: function () {
    return "g";
  },
}); // TypeError 

//       
obj.quaxxor = "the friendly duck"; //      
delete obj.foo; //      

// strict mode       TypeError 
function fail() {
  "use strict";
  delete obj.foo; // TypeError 
  obj.sparky = "arf"; // TypeEror 
}
fail();

// Object.defineProperty()     TypeError 
Object.defineProperty(obj, "ohai", { value: 17 }); // TypeErorr 
Object.defineProperty(obj, "foo", { value: "eit" }); //   

> Object.seal(1)
TypeError: 1 is not an object // ES5 code

> Object.seal(1)
1                             // ES6 code