Object.freeze()

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Metoda Object.freeze() "zamraża" obiekt, tzn. uniemożliwia dodawania nowych właściwości do obiektu, uniemożliwia usuwanie istniejących właściwości oraz uniemożliwia zmianę istniejących właściwości. W efekcie obiekt jest naprawdę stały.
 

Składnia

Object.freeze(obj)

Argumenty

obj
Obiekt który ma zostać "zamrożony".

Zwracana wartość

"Zamrożony" obiekt.

Opis

Nic nie może zostać dodane oraz usunięte z "zamrożonego" obiektu. Każda próba tego wywoła błąd, albo po cichu, albo rzucając wyjątek TypeError.

Values cannot be changed for data properties. Accessor properties (getters and setters) work the same (and still give the illusion that you are changing the value). Note that values that are objects can still be modified, unless they are also frozen.

Examples

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

// New properties may be added, existing properties may be changed or removed
obj.foo = 'baz';
obj.lumpy = 'woof';
delete obj.prop;

// Both the object being passed as well as the returned object will be frozen.
// It is unnecessary to save the returned object in order to freeze the original.
var o = Object.freeze(obj);

o === obj; // true
Object.isFrozen(obj); // === true

// Now any changes will fail
obj.foo = 'quux'; // silently does nothing
obj.quaxxor = 'the friendly duck'; // silently doesn't add the property

// ...and in strict mode such attempts will throw TypeErrors
function fail(){
  'use strict';
  obj.foo = 'sparky'; // throws a TypeError
  delete obj.quaxxor; // throws a TypeError
  obj.sparky = 'arf'; // throws a TypeError
}

fail();

// Attempted changes through Object.defineProperty will also throw
Object.defineProperty(obj, 'ohai', { value: 17 }); // throws a TypeError
Object.defineProperty(obj, 'foo', { value: 'eit' }); // throws a TypeError

The following example shows that object values in a frozen object can be mutated (freeze is shallow).

obj1 = {
  internal: {}
};

Object.freeze(obj1);
obj1.internal.a = 'aValue';

obj1.internal.a // 'aValue'

// To make obj fully immutable, freeze each object in obj.
// To do so, we use this function.
function deepFreeze(obj) {

  // Retrieve the property names defined on obj
  var propNames = Object.getOwnPropertyNames(obj);

  // Freeze properties before freezing self
  propNames.forEach(function(name) {
    var prop = obj[name];

    // Freeze prop if it is an object
    if (typeof prop == 'object' && prop !== null)
      deepFreeze(prop);
  });

  // Freeze self (no-op if already frozen)
  return Object.freeze(obj);
}

obj2 = {
  internal: {}
};

deepFreeze(obj2);
obj2.internal.a = 'anotherValue';
obj2.internal.a; // undefined

Notes

In ES5, if the argument to this method is not an object (a primitive), then it will cause a TypeError. In ES6, a non-object argument will be treated as if it were a frozen ordinary object, and be simply returned.

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

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

Specifications

Specification Status Comment
ECMAScript 5.1 (ECMA-262)
The definition of 'Object.freeze' in that specification.
Standard Initial definition. Implemented in JavaScript 1.8.5.
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'Object.freeze' in that specification.
Standard  
ECMAScript 2017 Draft (ECMA-262)
The definition of 'Object.freeze' in that specification.
Draft  

Browser compatibility

Feature Firefox (Gecko) Chrome Internet Explorer Opera Safari
Basic support 4.0 (2) 6 9 12 5.1
Feature Firefox Mobile (Gecko) Android IE Mobile Opera Mobile Safari Mobile
Basic support ? ? ? ? ?

See also

Autorzy i etykiety dokumentu

 Autorzy tej strony: piecioshka, aquz
 Ostatnia aktualizacja: piecioshka,