You don't have to use modernizr, but you can use their method to detect if localStorage is supported

modernizr at github

test for localStorage

// In FF4, if disabled, window.localStorage should === null.



// Normally, we could not test that directly and need to do a

//   `('localStorage' in window) && ` test first because otherwise Firefox will

//   throw bugzil.la/365772 if cookies are disabled



// Also in iOS5 & Safari Private Browsing mode, attempting to use localStorage.setItem

// will throw the exception:

//   QUOTA_EXCEEDED_ERRROR DOM Exception 22.

// Peculiarly, getItem and removeItem calls do not throw.



// Because we are forced to try/catch this, we'll go aggressive.



// Just FWIW: IE8 Compat mode supports these features completely:

//   www.quirksmode.org/dom/html5.html

// But IE8 doesn't support either with local files



Modernizr.addTest('localstorage', function() {

    var mod = 'modernizr';

    try {

        localStorage.setItem(mod, mod);

        localStorage.removeItem(mod);

        return true;

    } catch(e) {

        return false;

    }

});

updated with current source code