input 빈칸 체크

<script>
 function confirm(){
  var writeForm = document.writeForm;
  for(var i =0 ;i<writeForm.length;i++){  
   if(writeForm.elements[i].value == ""){ 
    window.alert("빈칸을 채워주세요");
    writeForm.elements[i].focus();
    return;
  }
  }
 }
</script>