HTML form with two submit buttons and two "target" attributes

It is more appropriate to approach this problem with the mentality that a form will have a default action tied to one submit button, and then an alternative action bound to a plain button. The difference here is that whichever one goes under the submit will be the one used when a user submits the form by pressing enter, while the other one will only be fired when a user explicitly clicks on the button.

Anyhow, with that in mind, this should do it:

<form id='myform' action='jquery.php' method='GET'>
    <input type='submit' id='btn1' value='Normal Submit'>
    <input type='button' id='btn2' value='New Window'>
</form>

With this javascript:

var form = document.getElementById('myform');
form.onsubmit = function() {
    form.target = '_self';
};

document.getElementById('btn2').onclick = function() {
    form.target = '_blank';
    form.submit();
}

Approaches that bind code to the submit button's click event will not work on IE.

I do this on the server-side. That is, the form always submits to the same target, but I've got a server-side script who is responsible for redirecting to the appropriate location depending on what button was pressed.

If you have multiple buttons, such as

<form action="mypage" method="get">

  <input type="submit" name="retry" value="Retry" />
  <input type="submit" name="abort" value="Abort" />

</form>

Note: I used GET, but it works for POST too

Then you can easily determine which button was pressed - if the variable retry exists and has a value then retry was pressed, and if the variable abort exists and has a value then abort was pressed. This knowledge can then be used to redirect to the appropriate place.

This method needs no Javascript.

Note: This question and answer was from so many years ago when "wanting to avoid relying on Javascript" was more of a thing than it is today. Today I would not consider writing extra server-side functionality for something like this. Indeed, I think that in most instances where I would need to submit form data to more than one target, I'd probably be doing something that justified doing a lot of the logic client-side in Javascript and using XMLHttpRequest (or indeed, the Fetch API) instead.