Asynchronous JavaScript and XML technique is for developing interactive web using combination of HTML,CSS and others for dynamic delivery of content to user. DoubleClick for Publishers is an example which currently supports Asynchronous JavaScript loading to make the page loading a faster process.
What is Asynchronous JavaScript Technology ?
In JavaScript, there are two ways to handle the HTTP requests primarily done through browser by an user – like loading of this webpage. They may be performed either loading synchronously or asynchronously. Synchronous means that the rest of the page loading execution process stops until that request has been performed. It is obvious that, this programming is simpler to do. JavaScript do not support multiple threading, that is the reason it needs to be loaded to full. Thus, no other operations can be carried out while waiting for a synchronous HTTP request. Now think that Javascript calls a server to display an Flash based Ad (bigger size) and in HTML code the placement is hierarchically higher than other components of the webpage to make it a viewable or readable to the reader.
Asynchronous JavaScript and XML (AJAX) is a kind of technology for dynamic web pages which allows the direct exchange and the representation of parts of web pages without the need of loading the entire web page. Ajax programs give the impression that they are running on the user’s computer. To avoid the problem with synchronous JavaScripts, asynchronous requests are used. This means that JavaScript in asynchronous does not waits for a response, but continues with the execution of the next line. In order to process the result of the request may still is passed to the request object also. This form is called asynchronous AJAX (Asynchronous JavaScript and XML).
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Other Notes on Asynchronous JavaScript
An asynchronous http request can be processed via the insertion of a SCRIPT Objects in the DOM tree, change of status is possible by change in a global variable or as described above in the property of an object. In some cases, the use of a synchronous method is preferable to an asynchronous one, it depends on the practical usage.
Example of Asynchronous JavaScript Technology
This is an example usage of asynchronous JavaScript technology by Google Analytics :
1 2 3 4 5 6 7 8 9 10 11 12 13 14 | <span style="color: #0000ff;"><script</span> type=<span style="color: #99cc00;">"text/javascript</span>"> var _gaq = _gaq || []; _gaq.push([<span style="color: #99cc00;">'_setAccount'</span>, <span style="color: #99cc00;">'UA-XXXXX-X'</span>]); _gaq.push([<span style="color: #99cc00;">'_trackPageview'</span>]); (<span style="color: #0000ff;">function</span>() { <span style="color: #0000ff;">var</span> ga = document.createElement(<span style="color: #99cc00;">'script'</span>); ga.type = <span style="color: #99cc00;">'text/javascript'</span>; ga.async = true; ga.src = (<span style="color: #99cc00;">'https:</span>' == document.location.protocol ? <span style="color: #99cc00;">'https://ssl'</span> : <span style="color: #99cc00;">'http://www'</span>) + '.google-analytics.com/ga.js'; <span style="color: #0000ff;">var</span> s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); <span style="color: #0000ff;"></script></span> |
As explained by Google, the first part of the asynchronous tracking code snippet assigns the _gaq variable to a JavaScript array. After that, two tracking API calls (encoded as arrays) are pushed onto _gaq. When the tracking code initializes, it transforms the _gaq object from a standard array into a new object and executes all the tracking API calls initially collected in the array. With this feature, you can immediately store all necessary tracking calls even before the Google Analytics tracking code is downloaded.
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