About AJAX

Posted by john
7/3/2007
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  Ajax from HTML, JavaScript ™ technology, DHTML DOM and composition, this method can be distinguished clumsy Web interface into the Ajax interactive applications.    This paper is the author of an Ajax expert, demonstrates how these technologies work together - from the overall outlined details of the discussion - to enable efficient Web development become a reality.    He also opened a Ajax core concept of mystery, including XMLHttpRequest object.    Five years ago, if we do not know XML, your attention is the ugly duckling no one.    18 months ago, has become the center of attention Ruby, Ruby programmers do not know the only bench.    Today, if the latest technology like fashion, that your goal is to Ajax.    However, Ajax is not just a fad, it is a powerful method of building sites, but not to learn a new language as difficult.    But Ajax in what is discussed in detail before, let us take a few minutes to understand what Ajax.    At present, the preparation of applications, there are two Basic options: desktop applications to Web applications they are similar, usually a desktop application for CD media (and sometimes can be downloaded from the site) and fully installed in your computer on.    Desktop application may use the Internet to download updates, but these applications run code on your desktop computer.    Web applications running on the Web server somewhere - not surprising, it is necessary to visit through a Web browser such applications.    However, the ratio of these applications run on the code where, more importantly, how the application operation and how its interactive.    General desktop applications quickly (in the running on your computer, do not have to wait for the Internet connection), a beautiful user interface (usually, and the operating system) and extraordinary dynamic.    You can click, select, import, open the menu and submenus, parades everywhere, basically do not need to wait.    On the other hand, Web applications are the latest trend, they provide can not be achieved on the desktop services (such as Amazon.com and eBay).    However, along with the Web is a powerful and waiting, waiting for the server response, waiting for the screen refresh and wait for the request to return and generate new pages.    Clearly say this was too sketchy, but the basic concept is so.    You may have already guessed, Ajax tried to build desktop application functionality and interactivity, and continually updated Web as a bridge between applications.    Can be used as common desktop applications and dynamic user interface controls and beautiful, but in the Web application.    Also, and so what?    We look at how Ajax clumsy Web interface will be translated into prompt response of Ajax app.    references), according to Jesse's explanation, this is not a first acronym.     Below are Ajax applications used by the basic technologies: html form for the creation of Web applications and determine the use of other parts of the field.    JavaScript code Ajax applications that run the core code, and to help improve the communication server applications.    Dynamic HTML, or DHTML, for dynamically updated form.    We will use div, span and other elements of dynamic HTML to mark HTML.    DOM for Document Object Model (through JavaScript code) handling of HTML structure and (under certain circumstances) to return to the XML server.    We further analysis of these technical functions.    After the article I will be in-depth discussion of these technologies, as long as familiar with these components and technology to it.    These familiar with the code, the easier it is from the fragmentation of these technologies to truly understand the changes to take advantage of these technologies (at the same time opened up a real Web application development door).    shown in a list.  
  the next section), handle HTML form server to return XML data structure.      For the first two points, need to be very familiar with getElementById () method, as shown in the list 2.  
  list 2 shows a simple JavaScript code, mixed with a small amount of HTML.      At the same time, but also with a little DOM, we at all times.     DOM Top  1 can be seen  from the list, and the creation and use of this object is very simple, is not it?      Wait.     Remember that a few years ago and those who hate the browser war?    Nothing in different browsers get the same result.    No matter whether you believe that the war is continuing, though on a smaller scale.    But it is strange that the XMLHttpRequest become one of the victims of this war.    Get XMLHttpRequest object may need to adopt a different approach.    Now I will explain in detail.     reference to further understand MSXML).      Therefore, if by Ajax applications and Internet Explorer to deal with, then we must use a special way to create objects.     It is not so simple.    According to Internet Explorer installed different versions of JavaScript technology, MSXML actually there are two different versions, it is necessary to prepare these two cases, namely code.     Please refer to the list 3, which Microsoft code in the browser to create a XMLHttpRequest.  
  the list  is a simple line as shown in the code:  var xmlHttp = new XMLHttpRequest object;.    This trip much simpler code in Mozilla, Firefox, Safari, Opera, as well as virtually all in any form or manner Ajax support non-Microsoft browser, created XMLHttpRequest object.    4 shows the list of such code.  
  Back to the top  in the world of 5 in the list of examples of Ajax approach is organized in accordance with this sequence:  
  5 5 in the list of the Ajax code that the ease of use.      Data is a simple text can be used as part of the request URL.      GET used rather than more complex POST send the request.      XML and did not want to add the contents of the head of the request did not want to send the data, in other words, this is the utopia of Ajax.     Not to worry, with the commencement of this series of articles, things will become more and more complex.    You will see how to send POST request, the request of the head and how to set up the type of content, how the information encoded in XML, and how to increase the safety of the request, can do the work of many!    To leave those temporary difficulties, and with good basic things on the trip, and soon we will establish a complete set of tools for Ajax.    6 in the list of examples of server available for under 5 in the list sent data call.  
  Top  Web 7 such  as a list  or use JavaScript technology bar.  
  参考资料中的那些文章了吧？   Top  those references in the article?      But could begin from these applications to the work of the basic concept, the XMLHttpRequest object to a basic understanding.      In the next issue of the article, you will grasp the object and learn how to deal with JavaScript and server communications, and how to use HTML form, and how to get DOM handle.     Now before we spend little time to consider the application Ajax consider how strong.    Imagine, when the click of a button, and enter a field, from the combo box, or choose an option on the screen by dragging the mouse, Web Forms will be able to immediately respond to what circumstances.    Asynchronous think what it means is, think about JavaScript code running it and not wait for the server to respond to the request.    What will encounter problems?    What will enter the field?    Given this new approach, the programmer should be the time to change the design of the form?    If these issues spend a little time with the simple shear / paste some code to your application simply do not understand the proceedings compared to income will be more.    In the next issue of the article, we will put into practice the concepts presented in detail the application of this method in accordance with the procedures required by the code work.    Therefore, the present first to enjoy the possibilities offered by the Ajax bar. 



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