html dom getelementbyid,HTML DOM getElementById()

HTML DOM getElementById()

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Développement de logiciels

13 déc. 2013 (il y a 7 années et 7 mois)

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Retranscription de la présentation

HTML DOM getElementById()

Method

The getElementById() method returns a

reference to the first object with the

specified ID.

Syntax

document.getElementById(id)

function getValue()

{

var x=document.getElementById("myHeader")

alert(x.innerH)

}

This is a header

Click on the header to alert its value

DHTML

http://www.midlandstech.com/edu/ed/ism/k

irkpatrick/dhtml.html

AJAX

Asynchronous JavaScript And XML

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.

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.

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/asynch

ronous.html



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.

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.



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.

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.

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.

Example



EW.com

poll

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.



Can compromise the accessibility of a site

for users with disabilities



Users unaccustomed to AJAX may have

learning curve.



AJAX is based on the XMLHttpRequest

object.



Different browsers use different methods

to create the XMLHttpRequest object.



Internet Explorer 5 and IE 6 use an Active

Object, while other browsers use the built

-

in JavaScript object called

XMLHttpRequest.

Example



http://www.midlandstech.com/edu/ed/ism

/kirkpatrick/ajax/ajaxquiz.html

Files used



Ajax.js



Questions.xml



Quiz.js



List17.4.js