tailieunhanh - Học JavaScript qua ví dụ part 91

Tại sao Ajax? JavaScript đã trải qua một thời kỳ Phục hưng kiểu riêng của mình kể từ khi cuốn sách này lần đầu tiên được xuất bản vào năm 2002 chủ yếu là do sự cường điệu và lời hứa của nó cung cấp. | chapter 18 An Introduction to Ajax with JSON Why Ajax JavaScript has gone through kind of a Renaissance of its own since this book was first published in 2002 largely due to the hype and promises it offers. Traditionally Web applications have been somewhat clumsy and slow and the level of interactivity and usability inferior to their counterpart desktop applications yet the number of Web applications available continues to grow at an amazing rate. Part of that growth has been spurred on by AJAX Asynchronous JavaScript and XML 1 not a new programming language but a methodology for creating fast rich user-friendly and interactive Web applications by allowing a Web page to request small fragments of information from the server instead of an entire page. In this approach asynchronous means that when a request is initiated by the occurrence of a client event JavaScript functions using Ajax allow the browser to interact in the background directly with the server and rather than waiting for the server to respond continue processing the page. The server will then send its response to Ajax containing only the data that needs changing. Ajax in turn will update that portion of the Web page. For example if you are filling out a form instead of waiting until all the fields have been filled and the page submitted now with Ajax the fields can be validated as they are filled and the user does not have to sit by waiting for the page to reload before continuing what he or she was doing. This process is shown in Figure . As discussed in Chapter 1 Introduction to JavaScript Google offers great examples of Ajax with Google Maps and Google Suggests an application shared now by all major browsers. In fact Ajax was made popular in 2005 with Google Suggest. When the you start searching in the Google search box each time you press a key Google lists items that fit that sequence of letters. In a drop-down list as if by magic words appear that contain those letters and after each .