A helper function to persist a value in local storage and update if that item is changed by another open window.

storageProxy.js

// helper function to persist the 
// changes to localStorage and
function storageProxy(key, updateFn){
	var store = window.localStorage;
	
	// udpate if the key is already set
	var initial = store.getItem(key);
	if(initial) updateFn(initial)

	// listen for updates from other windows
	window.addEventListener("storage", function(e){
		if(e.key == key) updateFn(e.newValue);
	}, false);
	
	// return a handle to update for this window
	return function(obj){
		store.setItem(key,JSON.stringify(obj));
		updateFn(obj);
	}
};


// usage :
// <a class="bgc" href="#f08">pink</a><a class="bgc" href="#08f">blue</a>
// 
// Background color will be persisted, and updated across all open windows
var bgColor = storageProxy('c-key', function(c){
	document.body.style.backgroundColor = c;
});
$(document).on('click', '.bgc', function(){
	bgColor($(this).attr('href'));
});