The last couple days have been a lot of fun. I was at LinuxWorld and did a book signing yesterday, my publisher had the first copies of Understanding AJAX at their booth. They should be showing up at bookstores and Amazon in the next couple weeks.
Your AJAX answers from my AJAX questions post are below, I hope everyone finds them helpful.
Dealing with broken connections
How can I find out whether a connection is broken? Should I just set a unique timeout per request after which an error message can be displayed? The timeout would be deactivated if the AJAX call succeeds. Is this a smart idea and does it work?
Using a timeout per request does work though its not a perfect solution. HTML_AJAX uses this approach, and a default timeout of 20 seconds. The issue is that 20 seconds is a long time to wait to provide an error, but there are still cases that hit this value. Its also hard to know what to do if you’ve hit an error, is this a transient failure and you should resend your request, or can you know longer talk to the server and you’re app needs to provide and error.
HTML_AJAX vs Prototype
CSS-style selectors, like those you use with the Behavior library gives you a good tool to write a degradable AJAX site, but the actual implementation can be pretty hard.
In general it means fully implementing a site without AJAX, then picking forms, links, etc that you want to make AJAX and tieing the AJAX too them at runtime. This works really well if your just doing something like type-ahead search since your not changing work flows, but it doesn’t always work that great for form submissions, since they often update different parts of the page, and the code that processes them is generally designed to build the whole page.
If your using AJAX for enhancements that don’t change the actual work flow then making your site degrable is easy. If your site relies on AJAX for its basic workflow you’ll have a much harder time making a site degrade.
AJAX File Upload
how can i make a file upload via ajax?
If you think of AJAX as involving using XMLHttpRequest then you can’t (at least not without disabling the browsers security model, which i don’t even recommend for intranet apps). But you can still upload files asyncronously, its just a matter of targeting a form at a hidden iframe. You will also want to look at generating your IFrame in JS since i believe it gives you less problems with browser history.
AJAX Form Submission
I’ve been studying AJAX for a bout a month now but I have not yet grasped the tecnique to submit a form with POST method. I’ve been trying to find an article that covered that but all I could find was the ones that included somekind of already made framework.
I want to know how to submit data to server (like form or email sending) with POST method.
Submit a POST request using AJAX you first have to understand what a normal form POST is.
When you submit a form in your browser it makes a http request with the following options:
HTTP Verb: POST
And a body of something like:
So to replicate a form POST in AJAX you need to run xmlhttp.open with POST set a header, xmlhttp.setRequestHeader(‘Content-type’,'application/x-www-form-urlencoded’);
Then encode your content and send it.
If you use a library most have code for handling this for you, HTML_AJAX has HTML_AJAX.formSubmit for taking a form and submitting it using AJAX and HTML_AJAX.post for doing custom POSTs.