On Thu, Feb 3, 2011 at 8:09 AM, Asen Bozhilov <asen.bozhi...@gmail.com>wrote:
> Juriy Zaytsev : > > > But is it a bug really? As far as I know, web storage spec ( > > http://dev.w3.org/html5/webstorage/) makes no clarification on whether > > interface members are writable; or enumerable/configurable for that > matter. > > WebIDL spec, however, does mention something about interface members > having > > attributes { [[Writable]]: true, [[Configurable]]: false, [[Enumerable]]: > > false } (http://dev.w3.org/2006/webapi/WebIDL/#es-interfaces). > > Thanks for the links and the info. > > > So it seems like writability of localStorage's getItem, setItem, clear, > etc. > > is actually in accordance to spec... which is probably not that great, > since > > it only makes for a more fragile implementation. The opposite argument > could > > be that [[writable]]: false would disallow "useful" cases of overwriting > > localStorage methods, whatever those cases might be. > > The problem is that they are not actually localStorage's methods. They > are inherited trough the prototype chain from `Storage' interface. > > localStorage.setItem('foo', 'bar'); > > localStorage.getItem = null; > > localStorage.getItem('foo'); //TypeError > > localStorage.__proto__.getItem.call(localStorage, 'foo'); //bar > > The setter in this case shadows `getItem' in the prototype chain and > here IMHO internal attributes wouldn't help a lot, while > `localStorage' instance hasn't own property `getItem'. > I think they have to specified the setter and getter of Storage instances. > So `setItem` sets keys on an object, shadowing interface members defined on the [[Prototype]]... Providing getItem/setItem shortcuts in terms of ES property access/assignment is always problematic, since objects are likely to inherit from `Object` (or other interfaces) and so can't be used as reliable "hash tables". It's the same shoot-in-the-foot-convenience, as providing access to elements via their id/name off of document (like IE did back in the days, and the rest followed the suit, if I recall correctly). Ditto for form controls exposed through the form. > > Another interesting part of `localStorage' are integer properties. For > example getter with integer is mimic of `localStorage.key(n)'; > > localStorage.setItem('foo', 'bar'); > > localStorage[0]; //returns foo > > localStorage[21]; //throws an Error with message: Index or size is > negative or greater than the allowed amount > > localStorage[-1]; > > This is about the getter, the more interesting part is. Could set an > item which key is integer digit? > > localStorage.setItem('10', 'bar'); > > localStorage.hasOwnProperty('10'); //true > > localStorage[10]; //Error try to get the 10th key instead of item with key > 10 > > localStorage.getItem('10'); //bar > > Another example using regular setter instead of `setItem': > > localStorage[666] = 'bar'; //There is not any errors here > > localStorage.getItem(666); //bar > > localStorage[666]; //Error > I didn't know numeric keys have special behavior. Is this part of the spec? That's one lovely interface... [...] -- kangax -- To view archived discussions from the original JSMentors Mailman list: http://www.mail-archive.com/jsmentors@jsmentors.com/ To search via a non-Google archive, visit here: http://www.mail-archive.com/jsmentors@googlegroups.com/ To unsubscribe from this group, send email to jsmentors+unsubscr...@googlegroups.com
