Ajax for client-server communication

This documentation describes the use of Ajax communication for standard Ebase facilities such as button clicks, hyperlink clicks, immediate validation requests etc. It does not include Ajax requests initiated from client-side Javascript added by the form developer. Ajax communication can be enabled or disabled by the developer, but cannot be configured in any other way.

How configured

Ajax communication between browser clients and the server can be configured via the Form Properties Dialog. The default setting for new forms is configured using the Designer Preferences Dialog.

How it works

When Ajax communication is enabled, Ajax is used wherever possible when posting data from the browser to the server and to return Html output to the browser. Only the minimum data representing and changed controls is sent back to the client on each occasion – this is referred to as an Incremental Page Refresh for the remainder of this document. This technique provides significant benefits when the same web page is redisplayed to the user: the transition is much smoother and the response time is faster. Smoother transitions provide an enhanced user interface which is more like a native application.

When Ajax communication is disabled, a traditional HTTP POST request is sent with each user request and the entire page is refreshed on each occasion – this is referred to as a Full Page Refresh for the remainder of this document.

There are many occasions where a Full Page Refresh is required e.g. the application logic routes control to another page or another form. When these situations are detected, the initial Ajax request is processed by the server, then the browser is requested to issue a Full Page Refresh request.

Back Button Considerations

The browser’s history cache (which the browser users for back button and forward button requests) is not updated when an Incremental Page Refresh is used. Therefore when Ajax is used successfully without the need for a Full Page Refresh, the user will not have the ability to return to the page before the request was made. Instead, the back button will return the user to the page resulting from the last Full Page Refresh. This situation will usually apply when the same page is redisplayed.

Use of JSPs with Ajax

When JSP are HTML files are configured on a page, either as top, left, right or bottom JSPs or in an Include Control, these are refreshed according to the setting of the static flag for each JSP or for the control: when a JSP is marked as static, it is not refreshed when that page is redisplayed e.g. as a result of an event such as a button click or field immediate validation. JSPs are always refreshed when moving to a different page. The static setting for a JSP can be configured at template level in the Form Default Properties or at form level in the Form Properties, or using the properties an Include Control.