main.js

//Context menu (new selection when right clicking page)
chrome.contextMenus.create({
	title: "Save page",
	contexts:["page", "selection", "link", "image", "video", "audio"],  // ContextType
	onclick: saveTab // A callback function
});

//Each saved url is saved as an individual object. So result returns an array of objects.
//Each object is a dictionary with the keys 'url' and 'url_short'
function saveTab(e) {
	//retrieve the old url_dict_list from local storage
	chrome.storage.local.get('urls', function(result) {
		console.log(result)
		var url_dict_list = []; //used to keep track of the dictionary for each url/url_short/jpg we hvae
		var url_list = []; //actual url from the dictionary
		if (!($.isEmptyObject(result))) //if returned object is not empty, append it to url_dict_list
		{
			var length = result['urls'].length;
			for (var i = 0; i < length; i++)
			{
				url_dict_list.push(result['urls'][i]);
				url_list.push(result['urls'][i]['url']);
				console.log(result['urls'][i]);
			}
		}
		//get the URL of the current tab and save it in the url_dict_list
		chrome.tabs.query({currentWindow: true, active: true}, function(tab) {
			var tab_url = tab[0].url;
			var url_short = tab[0].title;
			var url_icon = tab[0].favIconUrl
			var url_dict = {'url': tab_url, 'url_short': url_short, 'icon': url_icon};
			if ($.inArray(tab_url, url_list) == -1) //if current URL is not already saved
			{
				url_dict_list.push(url_dict);
				console.log(url_short);
				console.log('not already saved')
			}
			//first delete the old urls from storage, then add the new urls into storage
			chrome.storage.local.remove('urls', function() {
				//locally save url_dict_list (containing the new url)
				chrome.storage.local.set({'urls': url_dict_list}, function() {
					//callback function (maybe show that tab was successfully added)
				});
			});
		});	
	});
};