React drag/drop

gistfile1.js

dragStart: function(e) {
  this.setState({dragMouseStart: e.clientY, draggingElementId: e.currentTarget.getAttribute('data-slug')})
  e.dataTransfer.effectAllowed = 'move';
},
dragOver: function(e) {
  e.preventDefault();

  var over = e.currentTarget; // element we're hovering over
  var draggingId = this.state.draggingElementId;
  var toElId = over.getAttribute('data-slug');
  var movingUp = (this.state.dragMouseStart > e.clientY);

  if (draggingId != toElId) {
    orderCopy = this.state.artworksOrder
    var toIndex = orderCopy.indexOf(toElId)
    var fromIndex = orderCopy.indexOf(draggingId)
    if (movingUp) {
      orderCopy.splice(toIndex, 0, orderCopy.splice(fromIndex, 1)[0])
    } else {
      orderCopy.splice(fromIndex, 0, orderCopy.splice(toIndex, 1)[0])
    }
    this.setState({artworksOrder: orderCopy})
  }
}