On changing a value in
e.type === "storage"event should be fired in all other windows open to the same domain (e here being the event object seen by the event listener). (No specific mention forbids firing the same event in the same window, too, but it seems to be the intent to avoid that, to me, and is also the behaviour I would prefer myself.)
When an assignment (
e.keyproperty should be the name of the key, the
e.oldValueits former value, and
e.newValueits new value.
When a deletion (
e.newValueshould instead be the
When a clear all event (
e.newValueshould all be the
No browser seems to do quite that yet, but Safari and Chrome are at least rather close. My tests have covered Firefox 3.5.7, Safari 4.0.4 (6531.21.10), WebKit 4.0.4 (6531.21.10, r53119), Google Chrome 22.214.171.124 (35163) beta, Chromium 4.0.267.0 (34084), all on MacOS X (10.6). They all ignore which window triggered the storage event (= fire the event in all applicable windows).
Firefox, sadly, never provides either of the three properties mentioned above.
Chrome, Chromium, Safari and WebKit all provide all three, but instead of setting the
nullfor the clear event, it gets set to the empty string. The rest works beautifully, though.
Whether the clear event fires when clearing an already empty
localStoragevaries a little -- Firefox and Safari will, the others don't.
Neither browser fires events when deleting an already deleted value, but Firefox fires events when setting a property to the same value it already had (the others don't).
I spent a minimal amount of time peeking at what IE8 does and how, but didn't get it working. It supposedly supports at least the localStorage function-calling API, according to MSDN. The tests above may miss something subtle, maybe with how to use attachEvent instead of the W3C standard addEventListener (don't ask me why they still don't support that).