[hartz]

The point of standards for browsers is that you shouldn't need a polyfill just to support a feature (localStorage) in one browser. Ideally, it would just destroy its contents after your private browsing session is done, just like the way (I believe) all browsers treat cookies in private browsing mode.

[derefr]

Sure, what I'm saying is more that localStorage doesn't have the standards equivalent of an SLA guaranteeing it'll work for the "within the lifecycle of one page" use-case. Apple, I think, are just being opinionated (and pushy) here: they think the right way to tell a web-app "your localStorage won't save" is to undefine the API, making trying to write to or read from localStorage raise an exception, so that your app is then forced to decide whether it can go on without localStorage (by handling the exception, or by using a polyfill which does the same) or that it can't (by just telling the user "don't use this page in Private Browsing mode, doofus!" and stalling out.)

It's certainly not the approach everyone would be happy with, but it allows developers much more flexibility than the contrary case, where private browsing is a silent effect that might make apps do very stupid things (like, say, downloading the same huge asset bundle into localStorage over and over.)

[manigandham]

> downloading the same huge asset bundle into localStorage

This would happen anyway no matter what storage or cache is used since all data is cleared after private browsing session is over.

Breaking localstorage (with an over-quota error) is not the way to deal with this. Polyfills are just more crap in complexity and downloaded bytes to compensate for a browser's issues.

It would be much better to have a navigator.isPrivate flag enabled so apps can check the environment accurately, not guess based on whether certain APIs work or not. It's not about SLAs but supporting standards. Deleting client-side data is all that private browsing needs to do.