Edit in JSFiddle

function Box() {
  
  var animationStartTime = 0;
  var animationDuration = 500;
  var target = document.querySelector('.box');

  this.startAnimation = function () {
    animationStartTime = Date.now();
    requestAnimationFrame(update);
  };

  function update() {
    var currentTime = Date.now();
    var positionInAnimation = (currentTime - animationStartTime) / animationDuration;

    var xPosition = positionInAnimation * 100;
    var yPosition = positionInAnimation * 100;

    target.style.transform = 'translate(' + xPosition + 'px,' + yPosition + 'px)';

    if (positionInAnimation <= 1) {
      requestAnimationFrame(update);
    }
  }
}

var box = new Box();
box.startAnimation();


var b = document.querySelector('.box');
b.addEventListener('click', function () {
    box.startAnimation();
}, false);

html {
  background: #f2f2f2;
}

.box {
  width: 100px;
  height: 100px;
  background: #fff;
  box-shadow: 0 10xp 20px rgba(0,0,0,0.5);
}

@keyframes movingBox {
  0% {
    transform: translate(0, 0);
    opacity: 0.3;
  }

  25% {
    opacity: 0.9;
  }

  50% {
    transform: translate(100px, 100px);
    opacity: 0.2;
  }

  100% {
    transform: translate(30px, 30px);
    opacity: 0.8;
  }
}

<p>click to animate</p>
<div class="box"></div>