제이쿼리 요소 존재 확인, 자식요소존재 확인

1. length 사용

$('element').length == 0; // no element found

<div>
  <p>Here is a picture of me: </p>
  <img src="images/remy.jpg" />
  <div id="debug"></div>
</div>
<script type="text/javascript">
  if ($('img').length) { // implies *not* zero
    log('We found img elements on the page using "img"');
  } else {
    log('No img elements found');
  }
  
  if ($(':input').length != 0) {
    log('Found an input-type element using ":input"');
  } else {
    log('No input-type elements found');
  }
  
  log('Looking for "div img", found ' + $('div').find('img').length);
    
  function log(msg) {
    $('#debug').append('<p>' + msg + '</p>');
  }
</script>

2. not 과 has 를 쓴다

EX-

<span class="greenCheckMark"></span>

$('.clickedElement').live('click',function(){
//does the green check mark exist? if so then do nothing, else 
$('#listItem).append('<span class="greenCheckMark"></span>');
});




solution-

$('#listItem:not(:has(.greenCheckMark))')
    .append('<span class="greenCheckMark"></span>');




http://stackoverflow.com/questions/3365181/jquery-detect-if-element-exists