Why use a form tag when you're submitting via ajax?

Philosophical question:

Say I've got a web app that requires javascript and a modern browser, so progressive enhancement is not an issue. If my form is being built via javascript, and my data updates are all being done via ajax POSTs & PUTs, is there really any reason to wrap my controls in a form tag? If I'm still going to use the tag, say for semantic or structural reasons, is there any reason to have action and method params that I'm going to ignore? It kind of feels like a hold-over from an earlier era to me.

There is at least one important user-experience feature provided specifically by wrapping inputs inside a form tag:

The enter key will submit the form. In fact, in Mobile Safari, this is how you get the "Go" button to appear on the keyboard.

Without a form wrapping the inputs, there is nothing to submit.

You can of course provide enter-key behavior through a keypress event, but I don't know about if this works for mobile devices. I don't know about you, but I'd rather work with the semantics provided by the browser than have to imitate them with events.

In your case, you would simply provide an onsubmit event handler for the form, which would do your AJAX submit, then return false, canceling the actual submit.

You can simply provide action="" (which means "self"), and method is not required — it defaults to GET.

If you do not need progressive enhancement, you theoretically don't need them.

On the other hand, forms have some cool grouping and semantic effects. Using them, you can group your form elements logically, and make it easier for your scripts to gather the values of certain elements.

For example if you want to ajax-submit some user input, it is always easier to say: "let's take all elements in this form and submit them" than saying "let's take this input, these two selects and these three textareas and submit them". In my experience, it actually helps the developer if form tags are present.

AJAX is great but as JamWaffles (+1 to him) said, using form tags provides a fallback method.

Personally I use form tags, even for things I submit with AJAX because it is syntactically clear and makes it easy to grab all inputs within a specific form. Yes you could do this with a div or whatever too but as I said, using a form is syntactically nice.

Incidentally, screen readers treat the content inside a form differently so there are accessibility issues to be considered whichever way you choose to go. Note that anecdotal evidence suggests that Google considers accessibility in its rankings so if SEO is a concern for you, use a form and do it right.

Summary: forms OK for MVC, simple web apps, bad for component oriented, rich web apps.

Reason: forms cannot nest other forms: big limitation for a component-oriented architecture.

Details: For typical MVC applications, forms are great. In rich, complex web applications using a lot of javascript and AJAX and with a lot of components here and there, I don't like forms. Reason: forms cannot nest another forms. Then if each component renders a form, components cannot nest each other. Too bad. By changing all forms to divs, I can nest them, and whenever I want to grab all parameters in order to pass them to ajax, I just do (with jQuery):

$("#id_of_my_div").find("[name]").serialize();

(or some other filtering)

instead of:

$("#id_of_my_form").serialize();

Though, for sentimental and semantic reasons, I keep naming my divs something_form when they are acting as forms.

Not that I can see. I'm currently building a web application that uses <form>s, but I'm using them so I have a fallback method if the user has JavaScript disabled (an e.preventDefault stops the form posting normally). For your situation, where you're saying the user MUST have JavaScript, a <form> tag isn't necessary, but it might be an idea to keep it anyway in case browser need to do anything with it, or to access it as a sort of class.

In short, no, you don't need to use <form> if you're doing pure AJAX, although leaving it in might an idea if you suddenly decide to create fallback code in the future.

In my opinion: If you use it for semantic reasons, then use it as intended. The action attribute is required (also can be left empty) to be well-formed, also you can separate your URI-s from your js logic, by setting the action attribute, and reading it before the ajax call.

I don't see why you would need to use the form tag here. The only reason to use a form tag (other than to get your markup to validate) is if you are going to have the user "submit" the data using a sumbit input or button tag. If you don't need to do that, then there is no need for the form. However, not sure if it will be considered "valid" markup. If you do use it you can just do <form action=""> as action is the only required attribute of the form tag. However, you do bring up a good point, the future of web applications probably will no longer need the form and traditional submit methodology. Very interesting, and makes me happy. hehe :)