var textarea;
function deleteLine(ta){
  let startPos = ta.selectionStart;
  let endPos = ta.selectionEnd;
  let text = ta.value;
  let lStart = startPos-1;
  while(lStart>=0 && text.charAt(lStart)!='\n') lStart--;
  let lEnd = endPos;
  let len = text.length;
  while(lEnd<len && text.charAt(lEnd)!='\n') lEnd++;
  ta.value = text.substring(0,lStart+1) + text.substring(lEnd+1);
  ta.selectionStart = ta.selectionEnd = lStart +1;
}