tailieunhanh - Học JavaScript qua ví dụ part 93

Sử dụng Ajax để lấy từ một file XML XML là một ngôn ngữ đánh dấu mở rộng. Mặc dù tương tự như trong cấu trúc để HTML, XML được thiết kế để vận chuyển và lưu trữ dữ liệu, trong khi HTML được thiết kế để mô tả cách bố trí và màu sắc của những dữ liệu. | 822 Chapter 18 An Introduction to Ajax with JSON Figure A text file is retrieved and it contents displayed in a div container. Using Ajax to Retrieve XML from a File XML is the Extensible Markup Language. Although similar in structure to HTML XML was designed to transport and store data whereas HTML was designed to describe the layout and looks of the data. With XML you create markup that defines the structure of a document but instead of having predefined tags as with HTML you make your own. The XML tree looks similar to the HTML upside-down document tree starting with a root element at the top and branching down to parents attributes children and so on. XML has rules very XML-specific syntax rules on how to create a well-formed document. It is not hard to learn but if you are unfamiliar with XML go to the W3C schools Web site where you will find an excellent tutorial at http xml . XML data is often stored in external files as plain text. The data in the XML files can be easily exchanged between different programs applications and computers. In this chapter we are using Ajax to exchange data between a client and server. In the previous example the server returned a string of text from a simple text file. In this example we will use Ajax to get data from an XML file as an object and use the XML DOM to parse and display the data. And finally at the end of this chapter we will use an easier technology called JSON to make exchanging and parsing data a little simpler. In fact JSON is said to be rapidly replacing XML because of its easy lightweight data-interchange format. The XML file for the following example called is found in Example If you are not familiar with XML this file is a good example of how the markup is structured. The Ajax program Example makes a request to the server to get the XML file. The server returns an XML object and the rest of the program uses DOM methods and properties to .