immutability - Why would I need to freeze an object in JavaScript?

Question

It is not clear to me when anyone would need to use Object.freeze in JavaScript. MDN and MSDN don't give real life examples when it is useful. I get that part about not being able to change it at runtime which is enforced by a crash. The question is rather when would I appreciate a crash.

To me the immutability is a design time constraint which is supposed to be guaranteed by the type checker.

So is there any point in having a runtime crash in a dynamically typed language, besides detecting a violation better later than never?

question from:https://stackoverflow.com/questions/14791302/why-would-i-need-to-freeze-an-object-in-javascript

Answer 1

The Object.freeze function does the following:

• Makes the object non-extensible, so that new properties cannot be added to it.
• Sets the configurable attribute to false for all properties of the object. When - configurable is false, the property attributes cannot be changed and the property cannot be deleted.
• Sets the writable attribute to false for all data properties of the object. When writable is false, the data property value cannot be changed.

That's the what part, but why would anyone do this?

Well, in the object-oriented paradigm, the notion exists that an existing API contains certain elements that are not intended to be extended, modified, or re-used outside of their current context. The final keyword in various languages is the most suitable analogy of this. Even in languages that are not compiled and therefore easily modified, it still exists, i.e. PHP, and in this case, JavaScript.