var elements = document.querySelectorAll('.elem');

​

Array.from(elements).forEach(function(element) {

  var isActive = false;

  var isOver = false;

  element.addEventListener('pointerdown', function(event) {

    element.setPointerCapture(event.pointerId);

    element.classList.add('active');

    isActive = true;

    isOver = true;

  });

  element.addEventListener('pointerup', function() {

    element.classList.remove('active');

    isActive = false;

  });

  element.addEventListener('pointermove', function(event) {

    if (!isActive) {

      return;

    }

    var hoveredElement = event.target.ownerDocument.elementFromPoint(event.clientX, event.clientY);

    if (hoveredElement === element) {

      // Check the isOver flag to avoid unnecessary class operations

      if (!isOver) {

        isOver = true;

        element.classList.add('active');

      }

    } else {

      if (isOver) {

        isOver = false;

        element.classList.remove('active');

      }

    }

  });

});