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HTML DOM getElementById () Method

HTML DOM getElementById () Method. The getElementById () method returns a reference to the first object with the specified ID. Syntax document.getElementById (id) . <html> <head> <script type="text/ javascript "> function getValue () { var x= document.getElementById (" myHeader ")

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HTML DOM getElementById () Method

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  1. HTML DOM getElementById() Method The getElementById() method returns a reference to the first object with the specified ID. Syntax document.getElementById(id)

  2. <html> <head> <script type="text/javascript"> function getValue() { var x=document.getElementById("myHeader") alert(x.innerH) } </script> </head> <body> <h1 id="myHeader" onclick="getValue()">This is a header</h1> <p>Click on the header to alert its value</p> </body> </html>

  3. DHTML http://www.midlandstech.com/edu/ed/ism/kirkpatrick/dhtml.html

  4. AJAX Asynchronous JavaScript And XML

  5. AJAX is a type of programming made popular in 2005. AJAX is not a new programming language, but a new way to use existing standards combining JavaScript, CSS, HTML and XML.

  6. Asynchronous Not synchronized; that is, not occurring at predetermined or regular intervals. The term asynchronous is usually used to describe communications in which data can be transmitted intermittently rather than in a steady stream.

  7. For example, a telephone conversation is asynchronous because both parties can talk whenever they like. If the communication were synchronous, each party would be required to wait a specified interval before speaking. http://www.webopedia.com/TERM/A/asynchronous.html

  8. AJAX uses JavaScript’s capability to use a built-in object, XMLHttpRequest, to communicate with a web server without submitting a form or loading a page. It is supported by most modern browsers.

  9. Client-side - JavaScript • The script creates an XMLHttpRequest object and sends to the web server. • The server responds by sending the contents of a file, or the output of a server-side program.

  10. When the response arrives from the server, a JavaScript function is triggered to act on the data. • Because the goal is a more responsive user interface, the script usually displays the data from the server using the DOM, eliminating the need for a page refresh.

  11. Server-Side • The server responds to the client-side request by sending the contents of a file, or the output of a server-side program. • Not limited to XML on the server side. Can be a program running a language such as PHP, Perl, ASP.net, ColdFusion or even a static file.

  12. JavaScript can send data to a server-side program using GET or POST methods, the same two ways and HTML form works. In a GET request, the data is encoded in the URL that loads the program. In a post request, it is sent separately and can contain more data.

  13. Example • EW.com poll

  14. Limitations of AJAX • The script and the XML data or server-side program it requests data from must be on the same domain. • IE 6 uses ActiveX to implement XMLHttpRequest. Security settings in the browser must be set to allow ActiveX. • Older browsers don’t support XMLHttpRequest.

  15. Can compromise the accessibility of a site for users with disabilities • Users unaccustomed to AJAX may have learning curve.

  16. AJAX is based on the XMLHttpRequest object. • Different browsers use different methods to create the XMLHttpRequest object.

  17. Internet Explorer 5 and IE 6 use an Active Object, while other browsers use the built-in JavaScript object called XMLHttpRequest.

  18. Example • http://www.midlandstech.com/edu/ed/ism/kirkpatrick/ajax/ajaxquiz.html

  19. Files used • Ajax.js • Questions.xml • Quiz.js • List17.4.js

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