Select text and add to localstorage

Iv been using a simple html5 note taking application and would like to expand it.

I would like to be able to select some text and add that as a note . Im not sure if I would create a new function or amend one that already exists .

I have included the code below that I think adds the item to localstorage .

I have also included a link to the github page where the html code is : http://ift.tt/1DbZow9

if(newItem){ // don't push when generating from localStorage
            allTitles.push(listTitle);
            allLists.push({'title': listTitle, 'note': listNote});

            localStorage.setItem('allLists',JSON.stringify(allLists));
            localStorage.setItem('allTitles',allTitles);
        }

        return listContainer;
    };