Vanilla JS查找缺少子元素的元素

Question

I am trying to get a boolean that will let me know if a parent element has a child element. Some of the constraints are:

1. There can be x number of these "boxes"
2. Check and see for any of the boxes have a footer element

3. If the box does not have a footer element, add a class

   <div class="data-trend"> <header></header> <div class="main"></div> <footer></footer> </div>

   <div class="data-trend"> <header></header> <div class="main"></div> <footer></footer> </div>

   <div class="data-trend"> <header></header> <div class="main"> <span class="glyphicons"><span> <!-- On the glyphicons I would add class if there is no footer --> </div> <!-- notice no footer --> </div>

Answer 1

Moved the above comment into an actual answer:

 var elems = document.querySelectorAll('.data-trend'), len = elems.length, i = -1 while(++i < len) { if(!elems[i].querySelector('footer')) elems[i].classList.add('no-footer') } 

 .no-footer { border: 3px solid blue; } 

 <div class="data-trend"> <header>Testing</header> <div class="main"></div> <footer>Footer</footer> </div> <div class="data-trend"> <header>Testing</header> <div class="main"></div> <footer>Footer</footer> </div> <div class="data-trend"> <header>Testing</header> <div class="main"> <span class="glyphicons"><span> </div> </div> 

If you're doing a lot of this in vanilla, it makes sense to define a forEach helper function for yourself

function forEach(elems, fn){
  var len = elems.length,
      i = -1
  while(++i < len) {
    fn(elems[i])
  }
}