Cross-browser way to determine whether a DOM event was cancelled

Question

Is there a cross-browser way from a javascript event handler to determine whether the event has been cancelled by a previous handler? IE and other browsers like Chrome etc. have an event.returnValue property that can be tested, but FireFox doesn't appear to have any such property.

Here's an example of the scenario I'm talking about. You have a form like so:

<form id="test" name="test" onsubmit="return false;" />

And you hook up an event to it in javascript, with addEventListener/attachEvent (hookup ommitted for brevity). The event needs to know if anything prior in the chain returned false or otherwise canceled it. The IE version is like so:

function onSubmitHandler(e) {
    alert("event was cancelled prior to this handler: " + e.returnValue);
}

This works in IE, Chrome, etc., but of course not in FireFox as it doesn't have event.returnValue. I've combed the intarwebs for any other way to determine this in FireFox and come up with nothing. Is there a solution for this problem that doesn't involve setting the onsubmit attribute of the form directly?

Answer 1

My understanding is that the primary use of event.returnValue is to prevent the default action for that event (i.e. canceling it). For example, in a handler like yours above:

function onSubmitHandler(e) {
    e.returnValue = false;
}

The above code in IE would prevent the default action, preventing the form from being submitted. The equivalent code in Firefox, according to the Gecko DOM Reference, is:

e.preventDefault();

If you want to check if an event has been canceled, and do so in a cross-browser way, would using a library like jQuery be an option? Using jQuery to bind a function to the onsubmit event of the form and have that handler call .preventDefault() would accomplish the same thing across all supported browsers. Further, you could then use the .isDefaultPrevented() method of the jQuery event object to determine if the event has been canceled, presumably accomplishing what you are trying for with lhs = e.returnValue.

Answer 2

Here's the kludge way around this. I was hoping for a clean standards compliant method, but it appears there is none.

function onSubmitHandler()
{
    // only called if the other onsubmit handlers succeed
}

// hook in submit
var originalOnSubmit = form.onsubmit;

form.onsubmit = function(e)
{
    var ret;

    if (originalOnSubmit)
        ret = originalOnSubmit();

    if (ret != false)
    {
        return onSubmitHandler(e);
    }
};