• The sessionstorage object exists as a property of window object in supporting browsers. The sessionStorage object stores data that can persist for as long as window or tab is open.Even if you navigate away from page that stores the data and come back, the data saved to sessionStorage is still live.

• The sessionStorage is scoped to the document origin. The document origin is defined by its protocol, hostname, and port. The data stored in sessionStorage is tied to protocol, hostname, and port of the page that saved the information and only the same pages sharing the same protocol, hostname, and port can access the data later.

• The following urls has a different origins:

         http://www.sessionStorage.com        // Protocol: http;                                                                                      //hostname:www.example.com
         https://www.sessionStorage.com       // Different protocol
         http://static.sessionStorage.com     // Different hostname
         http://www.sessionStorage.com:8000   // Different port

• All document with same origin shares the same local storage data. They can read and ovewrite each other's data. But the documents with different origins can never read or overwrite each other's data.

• The sessionStorage is unique to a particluar window or tab. For example, suppose you open gmail in two different tabs of browser and application saves data in the sessionstorage. The data from the first tab is not accessible to other tab, even though the protocol, hostname, and port are exactly the same. Note that the sessionStorage is also scoped by browser vendor. If you visit a site using chrome and the visit the same using Firefox, then any data stored during first visit will not be accessible during the second visit.   

• The window based scoping of sessionStorage is only for top-level windows. If one browser tab contains two iframe element, and those iframe holds two document with same origin, then those two framed documents will share the session storage.

• The data stored in sessionStorage is deleted once the window or tab is closed, or if user request browser to do so. Such behaviour, with data tying to particular window or tab combined, ensures that the data does not get exposed or stored indefinitely.

• The data stored to sessionStorage is saved in key-value pairs where both the key and value are strings.

• getItem(key) - Returns a value on the basis of a specified key from the DOM storage area. If the key does not exist null is returned.
• setItem(key,value) - Stores a string value along with a specified key inside the DOM storage area.
• removeItem(key) - Removes a value on the basis of a specified key inside the DOM storage area.
• key(index) - Returns the key of a value at the specified index.
• clear() - Clears all data from the DOM storage area.

        sessionStorage.setItem("Name", "Thierry Henry");        // Store an string with the name "Name"
        sessionStorage.getItem("Name");           // Retrieve a value

        // Enumerate all stored name/value pairs
        for(var i = 0; i < sessionStorage.length; i++) {  // Length gives the # of pairs
            var name = sessionStorage.key(i);             // Get the name of pair i
            var value = sessionStorage.getItem(name);     // Get the value of that pair
        }

        sessionStorage.removeItem("Name");        // Delete the item "Name"
        
        sessionStorage.clear();                // Delete all keys from storage
        
        var count = sessionStorage.length;     // Gets the count of key-value pairs present in sessionStorage
    

• key - The name or key of the item that was set or removed. If the clear() method was called, this property will be null.

• newValue - Holds the new value of the item, or null if removeItem() was called.

• oldValue - Holds the old value of an existing item that changed or was deleted, or null if a new item was inserted.

• storageArea - This property will equal either the localStorage or the sessionStorage property of the target Window object.

• url - The URL (as a string) of the document whose script made this storage change.