There are the some demerits of using AJAX.
1. Development time
It usually requires more development time to build an application using AJAX than using other approaches.
2. Browsing history
If you use AJAX , there wont be any browsing history . So Back/ Forward button will be useless.
3. Cannot Bookmark the page
Data is loaded asynchronously without a page reload, so no page access is recorded in the browser history. This means that users are unable to easily bookmark or navigate to and from the application using the browser’s buttons.
4. Server load
Server load and bandwidth can be an issue when delivering AJAX-based solutions. These solutions often use AJAX to provide features like type-ahead searching in text boxes or loading data in the background. The user may see fewer page reloads, but the server calls are still there.
Like any other application that uses the HTTP protocol, data is sent as clear text. For this reason, sensitive data transfer via HTTP using AJAX is not secure.