I need to test whether the value of a form's onsubmit is a function. The format is typically onsubmit=return valid();. Is there a way to tell if this is a function, and if it's callable? Using typeof just returns that it's a string, which doesn't help me much.

EDIT: Of course, I understand that return valid(); is a string. I've replaced it down to valid();, and even valid(). I want to know if either of those is a function.

EDIT: Here's some code, which may help explain my problem:

$(a.button).parents(form).submit(function() {

    var submit_function = $(a.button).parents(form).attr(onsubmit);

    if ( submit_function && typeof( submit_function.replace(/return /,) ) == 'function' ) {

        return eval(submit_function.replace(/return /,));

    } else {

        alert(onSubmit is not a function.nnIs the script included?); return false;

    }

} );

EDIT 2: Here's the new code. It seems that I still have to use an eval, because calling form.submit() doesn't fire existing onsubmits.

var formObj = $(a.button).parents(form);

formObj.submit(function() {

    if ( formObj[0].onsubmit && typeof( formObj.onsubmit ) == 'function' ) {

        return eval(formObj.attr(onsubmit).replace(/return /,));

    } else {

        alert(onSubmit is not a function.nnIs the script included?);

        return false;

    }

} );

Suggestions on possibly how to do this better?