app.js

define(["require", "exports", "./Storage"], function(require, exports, Storage) {
    Storage.fetch();
});

app.ts

import Storage = require("./Storage");
Storage.fetch();

Storage.js

define(["require", "exports"], function(require, exports) {
    var Storage = (function () {
        function Storage() {
        }
        Storage.fetch = function () {
            if (!Storage.todos) {
                Storage.todos = JSON.parse(localStorage.getItem(Storage.STORAGE_KEY) || '[]');
            }
            return Storage.todos;
        };

        Storage.save = function () {
            localStorage.setItem(Storage.STORAGE_KEY, JSON.stringify(Storage.todos));
        };
        Storage.STORAGE_KEY = 'todos-vuejs';
        Storage.todos = null;
        return Storage;
    })();
    
    return Storage;
});

Storage.ts

class Storage{
    static STORAGE_KEY:string = 'todos-vuejs';
    static todos:any = null;

    static fetch(){
        if( !Storage.todos ){
            Storage.todos = JSON.parse( localStorage.getItem( Storage.STORAGE_KEY ) || '[]' );
        }
        return Storage.todos;
    }
    
    static save(){
        localStorage.setItem( Storage.STORAGE_KEY , JSON.stringify( Storage.todos ) );
    }
}
export = Storage;