Detecting localStorage v sessionStorage objects in different browsers

Question

I'm writing a Javascript class that is able to use either localStorage or sessionStorage. The selection of this is done on a class instance basis.

I have a method within this class, which receives the storage object as a parameter and runs an action according to the storage type (ie. local v session).

Eg.

function myMethod(store){
    // store: object storageObject
    //        The storage object being used (either
    //        sessionStorage or localStorage).

    if(store === sessionStorage){
        return sessionAction(store)
    }else if(store === localStorage){
        return localAction(store)
    }

    return null;
}

This does not work in Internet Explorer 8, producing the error: "Class doesn't support Automation". It seems to work in other browsers quite well.

I've tried to get the object type (via Object.prototype.toString.call(store)) and test against that but IE8 always reports [object Object] for this. I managed to make some progress from the answer to Stackoverflow question: Weird IE8 internal [[ class ]] attribute behavior. This workaround gave me [object Storage] in IE.

However, I still cannot detect between the different storage types. Is there a simple methodology for detecting between the two types that works cross-browser?

I could rewrite it so the type has't to be supplied as a parameter to the method. However, I'd rather reduce the simplicity of the API by allowing users to simply supply the storage object.

Answer 1

You can go aggressive for the IE8 code branch (inspired by Modernizr):

Compare storages:

function storagesEqual(testStorage, webStorage) {
    try {
        return testStorage === webStorage;
    } catch (ex) {
        // IE8 code branch
        var testKey = "storage-test";
        var testValue = (new Date()).valueOf().toString();
        var result = false;

        try {
            webStorage.setItem(testKey, testValue);
            if(testStorage[testKey] === testValue) {
                webStorage.removeItem(testKey);
                result = true;
            }
        } finally {
            return result;
        }
    }
}

Indetify storage type:

function storageType(store) {

    var STORAGE_LOCAL = 'local';
    var STORAGE_SESSION = 'session';
    var STORAGE_UNKNOWN = 'unknown';

    var localStorage = window.localStorage;
    var sessionStorage = window.sessionStorage;

    if(storagesEqual(store, localStorage)) return STORAGE_LOCAL;
    if(storagesEqual(store, sessionStorage)) return STORAGE_SESSION;
    return STORAGE_UNKNOWN;
}