Object.freeze() vs Object.seal() vs Object.preventExtension()

Object.freeze() vs Object.seal() vs Object.preventExtensions()

Methods seal, freeze, preventExtensions are used to make any object immutable.

Object.freeze()

The Object.freeze() method freezes an object.

1) Prevents adding new properties

2) Doesn’t allow remove existing properties

3) Does not allow to change immediate properties of object

4) Attributes of child objects can be modified

let obj = {

firstName:"sangram",

add:{

city:"mumbai"

}

}

Object.freeze(obj)

obj.firstName = "sagar"

delete obj.firstName

obj.lastName ="desai"

obj.add.city = "pune"

console.log("isFrozen",Object.isFrozen(obj))

console.log(obj)

Output:

isFrozen true

{ firstName: 'sangram', add: { city: 'pune' } }

Adding new property failed,deleting exiting property failed,modifying existig property fail ,updating child object property succeeded

we can freeze the arrays in JavaScript by using Object.freeze().

var a=["sagar","sangram"]

Object.freeze(a)

a.push("sanket")

GOT Error TypeError: Cannot add property 2, object is not extensible

Object.seal:

Seal method preventing new properties from being added to the object.

Allows changing existed properties of an object

Prevents adding new properties

Don’t allow remove existing properties

let obj = {

firstName:"sangram",

add:{

city:"mumbai",

state:"maharashtra"

}

}

Object.seal(obj)

obj.firstName = "sagar"

delete obj.firstName

obj.lastName ="desai"

obj.add.city = "pune"

delete obj.add.state

console.log("isSealed",Object.isSealed(obj))

console.log(obj)

Output:

isSealed true

{ firstName: 'sagar', add: { city: 'pune' } }

allowed to change child property & delete child property

Object.preventExtensions():

The Object.preventExtensions() method prevents new properties

from ever being added to an object (i.e. prevents future extensions

to the object). It does the following things:

Allows changing existed properties of an object

Prevents adding new properties

Feature	Default	Freeze	Seal	PreventExtension
Add New Property	Yes	No	No	No
Remove Existing Property	Yes	No	No	Yes
Change Existing Property Value	Yes	No	Yes	Yes
Modify Child Property	Yes	Yes	Yes	Yes

We can check a object has been applied preventExtension methos or not my using following method Object.isExtensible(objVariable);

Reverse effect of freeze,seal & preventExtension on Object

it is not possible to directly “unfreeze” or “unseal” an object that has been
frozen/sealed using the Object.freeze / Object.seal method in JavaScript. Once an
object has been frozen/sealed, it becomes immutable and cannot be changed.
However, it is possible to create a new object with the same or similar properties
Code: const originalStudent = { name: 'xyz', percentage: 85 }; const frozenStudent = Object.freeze(originalStudent); console.log(originalStudent) // Instead, create a new copy of object with the updated property const updatedObject = { ...frozenStudent }; console.log(Object.isFrozen(updatedObject)) // false console.log(updatedObject) Output: { name: 'xyz', percentage: 85 } false { name: 'xyz', percentage: 85 } Same thing can be done with sealed object too.