Object.preventExtensions()

Object.preventExtensions(obj)

// Object.preventExtensions 傳回一個被無法擴充的物件
var obj = {};
var obj2 = Object.preventExtensions(obj);
obj === obj2; // true

// 預設下，物件可以被擴充
var empty = {};
Object.isExtensible(empty); // === true

// ...但是以下情況之後，無法再被變更。
Object.preventExtensions(empty);
Object.isExtensible(empty); // === false

// Object.defineProperty throws 當為無法擴充的物件增加屬性
var nonExtensible = { removable: true };
Object.preventExtensions(nonExtensible);
Object.defineProperty(nonExtensible, "new", { value: 8675309 }); // throws a TypeError

// 在 strict mode 中，嘗試去新增屬性給無法擴充物件，將 throws 出一個 TypeError。
function fail() {
  "use strict";
  nonExtensible.newProperty = "FAIL"; // throws a TypeError
}
fail();

// EXTENSION (only works in engines supporting __proto__
// (which is deprecated. Use Object.getPrototypeOf instead)):
// A non-extensible object's prototype is immutable.
var fixed = Object.preventExtensions({});
fixed.__proto__ = { oh: "hai" }; // throws a TypeError

Object.preventExtensions(1);
// TypeError: 1 is not an object (ES5 code)

Object.preventExtensions(1);
// 1                             (ES6 code)