Object.freeze vs Object.seal in JavaScript | JavaScript interview Guide
ECMAScript 5 introduced new Object methods to Javascript. Among them seal, freeze, preventExtensions which can be used to make any object immutable.
So let see what does it exactly these methods will do and what are the differences between each of them.
Object.freeze()
The Object.freeze() method freezes an object. This is actually the most strict way of making objects immutable. It does the following things
prevents adding new properties
doesn’t allow remove existing properties
doesn't allow to change immediate properties of object
attributes of child objects can be modified
The result of calling Object.freeze(object) only applies to the immediate properties of object itself and will prevent future property addition, removal or value re-assignment operations only on object .
Even we can freeze the arrays in JavaScript by using Object.freeze()
With sealing, the situation is a little bit different, The Object.seal() method seals an object, preventing new properties from being added to the object. It does the following things
allows changing existed properties of an object
prevents adding new properties
don’t allow remove existing properties
An object called by this method can not have any new properties being added or current properties deleted.
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
Object.preventExtensions() marks an object as no longer extensible, so that it will never have properties beyond the ones it had at the time it was marked as non-extensible.
All three methods deal with the object’s immutability, which restricts adding new properties to it.
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