JS - Click Object and Change Class to Animate

HTML

<div class="circle"><a href=""></a></div>
<div class="circle"><a href=""></a></div>
<div class="circle"><a href=""></a></div>
<div class="circle"><a href=""></a></div>
<div class="circle"><a href=""></a></div>
<div class="circle"><a href=""></a></div>

JavaScript

document.addEventListener("DOMContentLoaded", function(event) {
var circles = document.getElementsByClassName("circle");

//keep track of the number of circle elements
var numCircles = circles.length;

//loop through the circles and place randomly
for (var i = 0; i < numCircles; i++) {

    //randomly choose top and left style properties
    circles[i].setAttribute('target','_blank');
    
}
});