| Summary: |
Most contemporary websites are not static but make use of text, imagery and data brought in from external sources. This means that the exact content of a page may not be known at the point that it is being designed and developed. For example a developer of a page which includes a weather forecast may be aware that it will include expected minimum and maximum temperatures,an icon summarising the weather conditions, and a short description but will not know exactly what is going to be displayed on any given day. In this case the actual data which will be displayed will be incorporated into the page from an external API at the point at which a request is made of the page to be displayed. It is possible to incorporate external data using either client or server side technologies. This presentation concentrates on client side technologies.
Many user interactions only manipulate small portions of the page but traditional techniques require that the entire page must be reloaded. Server responses contain the entire page content rather than just the portion being updated. Loading full pages typically results in several additional HTTP requests for images, style sheets, scripts, and any other content that may be on the page and so these can be slow. Currently Ajax is the most commonly used client side technique for loading data into a page from a server .
Ajax allows for HTTP communication without requiring an entire page refresh. Data is loaded into an object within a client side script (typically written in javaScript) and then integrated with the page content using DOM scripting techniques. Thus the web page can communicate with the server without refreshing the whole page.
An AJAX XMLHttpRequest is useless by itself, requires DOM scripting components to embed the received data into the current document . |
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