SO-34923221

by David Thomas

HTML

<div id="mydiv" class="a"></div>
<div id="myotherdiv"></div>

CSS

div {
  height: 2em;
  border: 3px solid limegreen;
  margin-top: 0.5em;
  border-radius: 1em 0;
}

.found {
  border-color: orange;
}

JavaScript

var div1 = document.querySelector("#mydiv"),
  div2 = document.querySelector('#myotherdiv'),
  div1HasClassName = div1.className.trim().length > 0,
  div2HasClassName = div2.className.trim().length > 0;

if (div1HasClassName) {
  div1.className += ' found';
}

if (div2HasClassName) {
  div2.className += ' found';
}