What are the differences between JavaScript's Object.freeze() and Object.seal() methods?

Antek N

TheObject.freeze() andObject.seal() methods in JavaScript are used to control the mutability and extensibility of objects. While both methods provide some level of object immutability, they have distinct differences in their behavior. Let's explore each method in detail: 1. Object.freeze(): - TheObject.freeze() method freezes an object, making it immutable. Once an object is frozen, you cannot add, remove, or modify its properties. Any attempts to do so will be silently ignored in non-strict mode, and will throw an error in strict mode. - The object's properties become read-only, preventing any changes to their values. - It also prevents changes to the object's prototype chain, ensuring that the object's structure remains unchanged. - Existing properties and their values remain intact and accessible. - Freezing an object is shallow, meaning that only the object itself is frozen, not its nested objects or arrays. - To check if an object is frozen, you can use theObject.isFrozen() method. 2. Object.seal(): - TheObject.seal() method seals an object, allowing modifications to its existing properties but preventing the addition or deletion of properties. - You can modify the values of existing properties, but you cannot add new properties or remove existing ones. - Sealing an object also makes its properties non-configurable, meaning you cannot change their attributes such asconfigurable,writable, orenumerable. - LikeObject.freeze(), sealing an object is shallow and does not affect nested objects or arrays. - To check if an object is sealed, you can use theObject.isSealed() method. In summary, the main differences betweenObject.freeze() andObject.seal() are: -Object.freeze() makes an object completely immutable, preventing any changes to its properties and structure, whileObject.seal() allows modifications to existing properties but prevents addition or removal of properties. -Object.freeze() makes the properties read-only, whileObject.seal() allows changes to property values. -Object.freeze() is more restrictive and provides stronger immutability thanObject.seal(), which still allows modifications to existing properties. It's important to note that bothObject.freeze() andObject.seal() only affect the object itself and its immediate properties, not the objects or arrays nested within it. To achieve deep immutability or sealing, you would need to recursively apply the methods to all nested objects and arrays.