Submit and onclick not working together

The best way is to call you method on the form tag like this:

<form onsubmit="return exefunction2();">
...
</form>

Returning false will not submit the form, true will submit!

to post more data (builded with exefunction2) you can use this

<script type="text/javascript">
    function exefunction2(form) {
        //add dynamic values
        var dynValues = {
            "val1": 1,
            "val2": "bla"
        };

        for(var name in dynValues) {
            //check if field exists
            var input = null;
            if(document.getElementsByName(name).length === 0) {
                input = document.createElement('input');
                input.setAttribute('name', name);
                input.setAttribute('type', 'hidden');
                form.appendChild(input);
            }
            else {
                input = document.getElementsByName(name)[0];
            }

            input.setAttribute('value', dynValues[name]);
        }
        return true;
    }
</script>

<form onsubmit="return exefunction2(this);">
    <input type="submit" />
</form>