Global Session Storage

Global Storage
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// ==UserScript==
// @name       Global Session Storage
// @namespace  http://legitspam.edu/
// @version    0.21
// @description  Global Storage
// @match      *://*/*
// @require	http://code.jquery.com/jquery-latest.js
// @author	http://blog.guya.net/2015/06/12/sharing-sessionstorage-between-tabs-for-secure-multi-tab-authentication/
// @grant	GM_getValue
// @grant	GM_setValue
// ==/UserScript==

var sessionStorage_transfer = function(event) {
    if(!event) { event = window.event; } // ie suq
    if(!event.newValue) return;          // do nothing if no value to work with
    if (event.key == 'getSessionStorage') {
        // another tab asked for the sessionStorage -> send it
        localStorage.setItem('sessionStorage', JSON.stringify(sessionStorage));
        // the other tab should now have it, so we're done with it.
        localStorage.removeItem('sessionStorage'); // <- could do short timeout as well.
    } else if (event.key == 'sessionStorage' && !sessionStorage.length) {
        // another tab sent data <- get it
        var data = JSON.parse(event.newValue);
        for (var key in data) {
            sessionStorage.setItem(key, data[key]);
        }
    }
};

// listen for changes to localStorage
if(window.addEventListener) {
    window.addEventListener("storage", sessionStorage_transfer, false);
} else {
    window.attachEvent("onstorage", sessionStorage_transfer);
};


// Ask other tabs for session storage (this is ONLY to trigger event)
if (!sessionStorage.length) {
    localStorage.setItem('getSessionStorage', 'foobar');
    localStorage.removeItem('getSessionStorage', 'foobar');
};