How do I sumbit a form with a textarea upon enter ?

function isEnterPressed(e,frm){
var keycode=null;
if (e!=null){
        if (window.event!=undefined){
                if (window.event.keyCode) keycode = window.event.keyCode;
                else if (window.event.charCode) keycode = window.event.charCode;              
        }else{
                keycode = e.keyCode;              
        }
}
if(keycode == 13)
{  
    document.forms["myform"].submit();
    document.getElementById('message').value="";
    document.getElementById('message').focus();
}
}
<form name="myform">
         <textarea name="message" id="message" onkeyup="if(isEnterPressed(event,this.form)){}" ></textarea>
</form>