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AJAX
Asynchronous JavaScript And XML
BTM 395: Internet Programming
Limitation of client-side programming
• Client-side programming (i.e. JavaScript)
cannot access the server directly
– No access to databases
– No reading or writing files on the server
– Only exception is content available to HTML, like
images and CSS
• Advantages are for security
– Protects web servers from malicious JavaScript
code
Limitation of server-side programming
• Server-side programming (e.g. PHP, ASP, JSP)
cannot access the client’s browser directly
– Once the web page is served, it cannot be changed further
– No interactive responses to user actions
– Any interaction requires reloading the page and responding
to GET, POST, cookies or sessions
• HTTP is a stateless protocol
– Once the server sends a page to the client, there is no active
connection maintained
– Thus the server cannot know what the client does until a
new page request is made
Ajax: marrying client- and server-side
web programming
• Ajax permits web clients to interact with the web
server without having to reload the entire page
• Basic procedure
– JavaScript creates an XMLHttpRequest (Ajax) object
– This Ajax object makes a call to a server-side script
• Normally, must be the same server that provided the HTML page, but
there are secure ways to get around this
– The Ajax object receives data in response
– The received data can be manipulated through JavaScript
• Raw Ajax coding is possible, but programmers
normally use frameworks like jQuery to make it
simpler