The WindowEventHandlers.onstorage property contains an event handler that runs when the storage event fires. This occurs when a storage area is changed (e.g. a new item is stored.)
Syntax
windowObj.onstorage = function() { ... };
Examples
window.onstorage = function(e) {
console.log('The ' + e.key + ' key has been changed from ' + e.oldValue + ' to ' + e.newValue + '.');
};