Most elegant way to check sessionStorage support?

function checkSessionStorage()
{
   return window.sessionStorage;
}

If it is undefined then sessionStorage is not supported.

I would use try/catch to check if the browser supports sessionStorage.

function isSessionStorageSupported() {
    try {
      var storage = window.sessionStorage;
      storage.setItem('test', 'test');
      storage.removeItem('test');    
      return true;
    } catch (e) {
      return false;
    }
}

Use the function like this:

 if (isSessionStorageSupported()) {
   // do something with it
 } else {
  // have a fallback code here
}

if (cookie1 === '9oz' || (window.sessionStorage && window.sessionStorage.getItem('sessionstoragecookie1') === '9oz')) {
    // you've got a 9oz reference 
} else {
    // you haven't :(
}

if(typeof(sessionStorage) == 'undefined')
{
    sessionStorage = {
        getItem: function(){},
        setItem: function(){},
        clear: function(){},
        removeItem: function(){}
    };
}

And now use as usual. It will always return NULL

But I would consider this script

http://code.google.com/p/sessionstorage/

This will enable sessionStorage in every browser.