CSS (Cascading Style Sheets) cung cấp một phương pháp thống nhất để kiểm soát sự xuất hiện của các yếu tố giao diện người dùng trong ứng dụng web của bạn. Bạn có thể sử dụng CSS để thay đổi gần như bất kỳ khía cạnh của cách trang ngoại hình, từ kích cỡ phông chữ, màu sắc, và khoảng cách, vị trí của các yếu tố. | Organizing the Code type text css head body body html Figure . The running application Organizing the Code All this new functionality will add a lot more complexity to our app so this is a good time to establish some kind of organization within our code a much better option than leaving everything in the global scope . After all we re building a fully functional AJAX application so we ll want to have it organized properly 43 Licensed to siowchen@ Chapter 3 The A in AJAX We ll use object-oriented design principles to organize our app. And we ll start of course with the creation of a base class for our application the Monitor class. Typically we d create a class in JavaScript like this function Monitor foo true function Do some stuff here This is a nice normal constructor function and we could easily use it to create a Monitor class or a bunch of them if we wanted to . Loss of Scope with setTimeout Unfortunately things will not be quite so easy in the case of our application. We re going to use a lot of calls to setTimeout as well as setInterval in our app so the normal method of creating JavaScript classes may prove troublesome for our Monitor class. The setTimeout function is really handy for delaying the execution of a piece of code but it has a serious drawback it runs that code in an execution context that s different from that of the object. We talked a little bit about this problem called loss of scope in the last chapter. This is a problem because the object keyword this has a new meaning in the new execution context. So when you use it within your class it suffers from a sudden bout of amnesia it has no idea what it is This may be a bit difficult to understand let s walk through a quick demonstration so you can actually see this annoyance in action. You might remember the ScopeTest class we looked at in the last chapter. To start with it was a simple class with one property and one method .
