I'm working on a client issue where Modernizr unexpectedly does not detect the support for the localStorage object in Internet Explorer 9. My page correctly uses the HTML 5 doctype (<!DOCTYPE html>) and the developer tools report the page has a Browser Mode of IE9 and a Document Mode of IE9 standards so I would expect this to work.
I've debugged into the following try/catch block in Modernizr and discovered a JavaScript error is thrown as soon as the localStorage object is accessed.
tests['localstorage'] = function() {
try {
localStorage.setItem(mod, mod);
localStorage.removeItem(mod);
return true;
} catch(e) {
return false;
}
};
On some machines the message of the JavaScript error is The system cannot find the file specified.. On others it is just Invalid argument. and Internet Explorer blocks for exactly 5 minutes before it throws the error.
What is causing accessing the localStorage object to throw an error here on Internet Explorer?
I've discovered if the lowest level subdomain matches one of the reserved device names as documented at Restrictions on the File Mask and File Name Properties on Internet Explorer then accessing the localStorage object will throw an error.
This problem is likely happening because internally Internet Explorer is attempting to access the file system using a reserved device name when accessing the localStorage object in order to satisfy the Storage object initialization steps.
It's certainly very much an edge case but if your page is comes from a server whose lowest level subdomain is exactly any of con, prn, aux, clock$, nul, com1, com2, com3, com4, com5, com6, com7, com8, com9, lpt1, lpt2, lpt3, lpt4, lpt5, lpt6, lpt7, lpt8, or lpt9 (e.g. http://prn.example.com) then this could well the reason why you are seeing this problem.
Choosing a lower level subdomain that wasn't a reserved device name in this situation solved the problem.