Instead of:
window.open("https://stackoverflow.com/questions/21461589/mailto:"+emailTo+'?cc="+emailCC+"&subject="+emailSub+"&body='+emailBody);
You can try:
location.href = "https://stackoverflow.com/questions/21461589/mailto:"+emailTo+'?cc="+emailCC+"&subject="+emailSub+"&body='+emailBody;