The disadvantages are: a)Ajax is not so friendly with search engine indexing because it uses Javascript for much part of its code. Search engines generally do not index Javascript present in web pages. b)Dynamically created pages created by ajax does not support back button which takes the user to the previous pages.
One big disadvantage of using AJAX is security. Often times developers do not put checks on the data coming into the server - they assume that it's coming from their own website. Unfortunately this is subject to injection attacks. Furthermore there is several ways to fake how the data is coming in making detection all but impossible.
The main disadvantages of using AJAX in a web application are: 1. Javascript dependency 2. View source is allowed and anyone can view the code source written for AJAX 3. Debugging is difficult. 4. Complexity of the code makes it difficult for web developers.
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